A composite activation method for synergistically improving surface roughness and cleanliness of strip steel before coating

Abstract

This invention discloses a composite activation method for synergistically improving the surface roughness and cleanliness of steel strips before coating, relating to the field of metal material surface treatment technology. The invention includes conveying the steel strip to be treated to a pre-cleaning station. By compounding an acidic activating component, a surface-active component, a dispersing and stabilizing component, and hard microparticles to form a composite activation medium, the invention continuously treats the steel strip surface in a pre-spraying zone, a particle-carrying brushing zone, and a renewal spraying zone, achieving a synergistic effect of chemical activation and mechanical micro-abrasion. The activation liquid weakens the interfacial bonding strength between the oxide layer, attached contaminants, and the steel strip substrate. The hard microparticles, driven by the brushing components, micro-abrade and peel off the activated surface area, improving the removal efficiency of the oxide layer and stubborn contaminants on the steel strip surface. Simultaneously, it forms a micro-rough surface suitable for coating adhesion, improving the surface roughness and cleanliness of the steel strip before coating.

Description

Technical Field

[0001] This invention belongs to the field of metal material surface treatment technology, and in particular relates to a composite activation method that synergistically improves the surface roughness and cleanliness of steel strips before coating. Background Technology

[0002] Steel strip is widely used in appliance panels, building materials, automotive parts, and functional coated products. Pre-coating treatment is a fundamental process in steel strip surface manufacturing, and the surface condition after pre-treatment affects coating adhesion, film uniformity, and performance stability. Existing steel strip pre-coating processes mainly include degreasing and cleaning, surface cleaning, oxide layer removal, activation treatment, and surface roughening. Common methods include chemical degreasing, electrolytic cleaning, water washing, acid pickling and activation, mechanical brushing, abrasive treatment, and chemical conversion treatment. Chemical cleaning primarily removes rolling oil, fingerprints, and fine particles. Mechanical treatment mainly adjusts the surface microstructure, creating a certain undulating structure on the steel strip surface. Chemical activation mainly improves the surface reaction state and enhances the interfacial interaction between the substrate and subsequent treatment solutions and coatings. Continuous steel strip production lines generally arrange processing units in a predetermined sequence, combining spraying, immersion washing, roller brushing, or electrochemical methods to adapt to the requirements of different steel grades, plate shapes, and coating systems for pre-treatment surfaces. As the requirements for adhesion performance, corrosion resistance and appearance consistency of coated products continue to increase, the pretreatment process for strip coating is gradually developing towards refinement, continuity and stabilization, and surface condition control has also become an important factor affecting product quality.

[0003] The core flaw of existing technology is that it is difficult to improve surface roughness and surface cleanliness simultaneously in the same processing stage. The improvement of surface roughness and surface cleanliness usually depends on different processing mechanisms and different process units. The treated strip steel surface often only meets the requirements in a single indicator, and it is difficult to form a micro-morphology that is conducive to mechanical interlocking of the interface and a clean and stable bonding interface at the same time. As a result, there is a lack of stable bonding foundation between the subsequent coating and the substrate, and it is difficult to maintain consistent coating quality. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a composite activation method for synergistically improving the surface roughness and cleanliness of steel strips before coating. The technical problem this invention aims to solve is: how to address the difficulty in synergistically improving the surface roughness and surface cleanliness of steel strips before coating, which leads to a lack of stable bonding between the coating and the substrate, through a composite activation method process including pre-cleaning, preparation of composite activation media, pre-spraying-particle brushing-renewal spraying synergistic treatment, rinsing, and drying.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a composite activation method for synergistically improving the surface roughness and cleanliness of steel strips before coating, comprising:

[0006] S1. The strip steel to be processed is conveyed to the pre-cleaning station, and the surface of the strip steel to be processed is degreased and cleaned to remove free oil and loose impurities from the surface of the strip steel, so as to obtain pre-cleaned strip steel.

[0007] S2. The acidic activating component, the surface-active component, and the dispersion stabilizing component are added to a liquid medium and mixed to obtain an activating solution; hard microparticles are added to the activating solution and dispersed to obtain a composite activating medium;

[0008] S3. The pre-cleaned strip is conveyed to the composite activation station, which is sequentially configured with a pre-spraying zone, a particle-carrying brushing zone, and a renewal spraying zone along the conveying direction of the pre-cleaned strip. In the pre-spraying zone, the composite activation medium is sprayed onto the surface of the pre-cleaned strip, forming a medium film layer containing the activation liquid and the hard particles on the surface of the pre-cleaned strip. In the particle-carrying brushing zone, while the medium film layer continuously covers the surface of the pre-cleaned strip, a brushing component is used to brush the surface of the pre-cleaned strip, and the activation liquid acts on the pre-cleaned strip. The interface between the oxide layer and attached contaminants on the surface and the substrate is reduced to decrease the interfacial bonding strength between the oxide layer and attached contaminants and the substrate. The hard particles, driven by the brushing component, perform micro-abrasion and stripping treatment on the same surface area treated by the activation liquid. In the renewal spraying zone, the composite activation medium is continued to be sprayed onto the strip surface treated by the particle-carrying brushing zone to renew the medium film layer on the strip surface and remove the stripping material and residual medium formed during the brushing process. The redeposition of the stripping material in the micro-depressions on the surface formed by micro-abrasion is inhibited, resulting in a composite activated strip.

[0009] S4. The composite activated strip is conveyed to the rinsing station, and the surface of the composite activated strip is rinsed to remove the residual composite activation medium and stripping material on the surface of the strip, so as to obtain the rinsed strip.

[0010] S5. The rinsed strip is conveyed to the drying station and the surface of the rinsed strip is dried to obtain strip before coating.

[0011] The present invention is further configured such that the pre-cleaning station is cleaned by spraying with an alkaline degreasing solution, the temperature of which is 45℃-60℃; and the spraying time is 8s-20s.

[0012] The present invention is further configured such that the acidic activating component is selected from one of phosphoric acid, citric acid and oxalic acid, the surfactant component is selected from one of nonionic surfactant and anionic surfactant, and the dispersion stabilizing component is selected from one of polyacrylate, hexametaphosphate and polycarboxylate.

[0013] The present invention is further configured such that the liquid medium is deionized water and the pH value of the activation solution is 1.5-5.5.

[0014] The present invention is further configured such that the mass fraction of the acidic activating component in the activating solution is 1%-10%, the mass fraction of the surface active component in the activating solution is 0.1%-2%, and the mass fraction of the dispersion stabilizing component in the activating solution is 0.05%-1.5%.

[0015] The present invention is further configured such that the hard microparticles are selected from one of alumina, silicon carbide, silicon dioxide and cerium oxide, the average particle size of the hard microparticles is 1μm-10μm, and the mass fraction of the hard microparticles in the composite activation medium is 0.5%-5%.

[0016] The present invention is further configured such that the dispersion is carried out by mechanical stirring, and the dispersion time is 10 min-20 min; the composite activation medium is circulated and transported between the pre-spraying zone, the particle-carrying brushing zone and the renewal spraying zone.

[0017] The present invention is further configured such that the injection pressure of the composite activation medium in the pre-injection zone and the renewal injection zone is 0.2MPa-0.5MPa.

[0018] The present invention is further configured such that the brushing component is a nylon roller brush, the rotation speed of the nylon roller brush is 200rpm-600rpm, and the residence time of the pre-cleaned strip steel in the composite activation station is 10s-40s.

[0019] The present invention is further configured such that the rinsing station includes two-stage rinsing units, the first-stage rinsing unit uses process water spray rinsing, and the second-stage rinsing unit uses deionized water spray rinsing; the drying process is carried out by air knife blowing and hot air drying in sequence, the hot air temperature is 100℃-140℃, and the drying time is 5s-15s.

[0020] The beneficial effects of this invention are as follows: This invention forms a composite activation medium by combining acidic activating components, surface-active components, dispersion stabilizing components, and hard microparticles, and continuously treats the strip steel surface in the pre-spraying zone, particle-carrying brushing zone, and renewal spraying zone, achieving a synergistic effect of chemical activation and mechanical micro-erosion; wherein, the activation liquid can weaken the interfacial bonding strength between the oxide layer, attached contaminants, and the strip steel substrate, and the hard microparticles, driven by the brushing components, perform micro-erosion and peeling on the activated surface area, improving the removal efficiency of the oxide layer and stubborn contaminants on the strip steel surface, while forming a micro-rough surface suitable for coating adhesion, improving the roughness and cleanliness of the strip steel surface before coating.

[0021] This invention employs a combined treatment method of pre-spraying, particle-carrying brushing, and renewal spraying, which enables the composite activating medium to continuously form an effective medium film layer on the surface of the strip steel. After brushing, the stripping material and residual medium are promptly renewed and removed, reducing the redeposition of stripping material in the micro-depressions on the surface formed by micro-abrasion. At the same time, the subsequent two-stage rinsing, air knife blowing, and hot air drying further remove residual activating medium and stripping material, ensuring that the strip steel surface is clean and dry, which is beneficial to improving the adhesion, uniformity, and coating quality stability of subsequent coatings. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0023] Figure 1 This is a flowchart of the overall process of the present invention.

[0024] Figure 2 This is a flowchart illustrating the preparation process of the composite activation medium of the present invention.

[0025] Figure 3 This is a schematic diagram of the composite activation station structure and media circulation of the present invention.

[0026] Figure 4 This is a schematic diagram of the rinsing station structure of the present invention.

[0027] Figure 5 This is a schematic diagram of the drying station structure of the present invention. Detailed Implementation

[0028] The technical solutions of the present invention will be described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0029] Example 1

[0030] Please see Figures 1-5 This invention relates to a composite activation method for synergistically improving the surface roughness and cleanliness of steel strips before coating, comprising:

[0031] S1. The strip steel to be processed is conveyed to the pre-cleaning station, where its surface is degreased and cleaned to remove free oil and loose impurities, resulting in pre-cleaned strip steel. The pre-cleaning station uses an alkaline degreasing solution spray cleaning at a temperature of 48℃. The spraying time is 10 seconds.

[0032] S2. The acidic activating component, the surfactant component, and the dispersion stabilizing component are added to a liquid medium and mixed to obtain an activation solution. Hard microparticles are then added to the activation solution and dispersed to obtain a composite activation medium. The acidic activating component is citric acid, the surfactant component is a nonionic surfactant, and the dispersion stabilizing component is polyacrylate. The liquid medium is deionized water, and the pH of the activation solution is 4.5. The mass fraction of the acidic activating component in the activation solution is 3%, the mass fraction of the surfactant component is 0.5%, and the mass fraction of the dispersion stabilizing component is 0.3%. The hard microparticles are silica, with an average particle size of 3 μm, and their mass fraction in the composite activation medium is 1.5%. Dispersion is carried out by mechanical stirring for 12 minutes.

[0033] S3. The pre-cleaned strip is conveyed to the composite activation station, which is sequentially set up with a pre-spraying zone, a particle-carrying brushing zone, and a renewal spraying zone along the conveying direction of the pre-cleaned strip. In the pre-spraying zone, the composite activation medium is sprayed onto the surface of the pre-cleaned strip, forming a medium film layer containing activation liquid and hard particles on the surface of the pre-cleaned strip. In the particle-carrying brushing zone, while the medium film layer continuously covers the surface of the pre-cleaned strip, the surface of the pre-cleaned strip is brushed using a brushing component. The activation liquid acts on the interface between the oxide layer and the attached contaminants on the surface of the pre-cleaned strip to reduce the interfacial bonding strength between the oxide layer and the attached contaminants and the substrate. The hard particles, driven by the brushing component, perform micro-abrasion and peeling treatment on the same surface area that has been treated by the activation liquid. In the renewal spray zone, the composite activation medium continues to be sprayed onto the surface of the strip steel treated in the particle-carrying brushing zone, renewing the medium film layer on the strip steel surface and removing the sludge and residual medium formed during the brushing process. This inhibits the redeposition of sludge in the microscopic depressions on the surface formed by micro-abrasion, resulting in composite-activated strip steel. The composite activation medium is circulated between the pre-spraying zone, the particle-carrying brushing zone, and the renewal spraying zone. The spraying pressure of the composite activation medium in the pre-spraying zone and the renewal spraying zone is 0.25 MPa. The brushing component is a nylon roller brush, and the rotation speed of the nylon roller brush is 300 rpm. The residence time of the pre-cleaned strip steel in the composite activation station is 15 seconds.

[0034] S4. The composite activated strip is conveyed to the rinsing station, where the surface of the composite activated strip is rinsed to remove residual composite activation medium and stripping material, resulting in rinsed strip. The rinsing station includes two rinsing units: the first rinsing unit uses process water spray rinsing, and the second rinsing unit uses deionized water spray rinsing.

[0035] S5. The rinsed strip steel is conveyed to the drying station, and the surface of the rinsed strip steel is dried to obtain the strip steel before coating. The drying process is carried out by air knife blowing and hot air drying in sequence. The hot air temperature is 110℃ and the drying time is 7s.

[0036] In this embodiment, the free oil, loose particles, and slight oxide layer on the surface of the strip steel before coating are effectively removed, and a finer and more uniform micro-uneven structure is formed on the surface. The surface roughness is improved more gradually, and local excessive abrasion is less likely to occur. The resulting strip steel surface is more inclined to be clean and improved. It is suitable for strip steel pretreatment scenarios with low original surface contamination, thin oxide layer, thin subsequent coating, or high requirements for surface smoothness.

[0037] Example 2

[0038] Please see Figures 1-5 Based on Example 1, a composite activation method for synergistically improving the surface roughness and cleanliness of steel strips before coating includes:

[0039] S1. The strip steel to be processed is conveyed to the pre-cleaning station, where its surface is degreased and cleaned to remove free oil and loose impurities, resulting in pre-cleaned strip steel. The pre-cleaning station uses an alkaline degreasing solution spray cleaning at a temperature of 52℃. The spraying time is 14 seconds.

[0040] S2. The acidic activating component, surfactant component, and dispersion stabilizing component are added to a liquid medium and mixed to obtain an activation solution. Hard microparticles are then added to the activation solution and dispersed to obtain a composite activation medium. The acidic activating component is phosphoric acid, the surfactant component is an anionic surfactant, and the dispersion stabilizing component is hexametaphosphate. The liquid medium is deionized water, and the pH of the activation solution is 3.5. The mass fraction of the acidic activating component in the activation solution is 5%, the mass fraction of the surfactant component is 1%, and the mass fraction of the dispersion stabilizing component is 0.7%. The hard microparticles are alumina with an average particle size of 5 μm, and the mass fraction of the hard microparticles in the composite activation medium is 3%. Dispersion is carried out by mechanical stirring for 15 min.

[0041] S3. The pre-cleaned strip is conveyed to the composite activation station, which is sequentially set up with a pre-spraying zone, a particle-carrying brushing zone, and a renewal spraying zone along the conveying direction of the pre-cleaned strip. In the pre-spraying zone, the composite activation medium is sprayed onto the surface of the pre-cleaned strip, forming a medium film layer containing activation liquid and hard particles on the surface of the pre-cleaned strip. In the particle-carrying brushing zone, while the medium film layer continuously covers the surface of the pre-cleaned strip, the surface of the pre-cleaned strip is brushed using a brushing component. The activation liquid acts on the interface between the oxide layer and the attached contaminants on the surface of the pre-cleaned strip to reduce the interfacial bonding strength between the oxide layer and the attached contaminants and the substrate. The hard particles, driven by the brushing component, perform micro-abrasion and peeling treatment on the same surface area that has been treated by the activation liquid. In the renewal spray zone, the composite activation medium continues to be sprayed onto the surface of the strip steel treated in the particle-carrying brushing zone, renewing the medium film layer on the strip steel surface and removing the sludge and residual medium formed during the brushing process. This inhibits the redeposition of sludge in the microscopic depressions on the surface formed by micro-abrasion, resulting in composite-activated strip steel. The composite activation medium is circulated between the pre-spraying zone, the particle-carrying brushing zone, and the renewal spraying zone. The spraying pressure of the composite activation medium in the pre-spraying zone and the renewal spraying zone is 0.35 MPa. The brushing component is a nylon roller brush, and the rotation speed of the nylon roller brush is 400 rpm. The residence time of the pre-cleaned strip steel in the composite activation station is 25 seconds.

[0042] S4. The composite activated strip is conveyed to the rinsing station, where the surface of the composite activated strip is rinsed to remove residual composite activation medium and stripping material, resulting in rinsed strip. The rinsing station includes two rinsing units: the first rinsing unit uses process water spray rinsing, and the second rinsing unit uses deionized water spray rinsing.

[0043] S5. The rinsed strip steel is conveyed to the drying station, and the surface of the rinsed strip steel is dried to obtain the strip steel before coating. The drying process is carried out by air knife blowing and hot air drying in sequence. The hot air temperature is 120℃ and the drying time is 10s.

[0044] In this embodiment, the oil, adhering impurities, and oxides on the surface of the strip steel before coating can be more fully activated, peeled off, and carried out. The surface cleanliness and micro-roughness are improved simultaneously, and the surface state is more balanced. This not only ensures a good clean base but also provides a stable adhesion interface for the coating. The resulting strip steel surface is more inclined to be a type with synergistic improvement in cleanliness and roughness, which is suitable for general processing scenarios such as conventional cold-rolled strip steel, pre-plating, or pre-coating.

[0045] Example 3

[0046] Please see Figures 1-5 Based on Examples 1 and 2, a composite activation method for synergistically improving the surface roughness and cleanliness of steel strips before coating includes:

[0047] S1. The strip steel to be processed is conveyed to the pre-cleaning station, where its surface is degreased and cleaned to remove free oil and loose impurities, resulting in pre-cleaned strip steel. The pre-cleaning station uses an alkaline degreasing solution spray cleaning at a temperature of 56℃. The spraying time is 18 seconds.

[0048] S2. The acidic activating component, surfactant component, and dispersion stabilizing component are added to a liquid medium and mixed to obtain an activation solution. Hard microparticles are then added to the activation solution and dispersed to obtain a composite activation medium. The acidic activating component is oxalic acid, the surfactant component is a nonionic surfactant, and the dispersion stabilizing component is a polycarboxylate. The liquid medium is deionized water, and the pH of the activation solution is 2.8. The mass fraction of the acidic activating component in the activation solution is 7%, the mass fraction of the surfactant component is 1.5%, and the mass fraction of the dispersion stabilizing component is 1%. The hard microparticles are silicon carbide, with an average particle size of 7 μm, and the mass fraction of the hard microparticles in the composite activation medium is 4%. Dispersion is carried out by mechanical stirring for 18 minutes.

[0049] S3. The pre-cleaned strip is conveyed to the composite activation station, which is sequentially set up with a pre-spraying zone, a particle-carrying brushing zone, and a renewal spraying zone along the conveying direction of the pre-cleaned strip. In the pre-spraying zone, the composite activation medium is sprayed onto the surface of the pre-cleaned strip, forming a medium film layer containing activation liquid and hard particles on the surface of the pre-cleaned strip. In the particle-carrying brushing zone, while the medium film layer continuously covers the surface of the pre-cleaned strip, the surface of the pre-cleaned strip is brushed using a brushing component. The activation liquid acts on the interface between the oxide layer and the attached contaminants on the surface of the pre-cleaned strip to reduce the interfacial bonding strength between the oxide layer and the attached contaminants and the substrate. The hard particles, driven by the brushing component, perform micro-abrasion and peeling treatment on the same surface area that has been treated by the activation liquid. In the renewal spray zone, the composite activation medium continues to be sprayed onto the strip surface treated in the particle-carrying brushing zone, renewing the medium film layer on the strip surface and removing the sludge and residual medium formed during the brushing process. This inhibits the redeposition of sludge in the micro-depressions formed by micro-abrasion, resulting in a composite-activated strip. The composite activation medium is circulated between the pre-spraying zone, the particle-carrying brushing zone, and the renewal spraying zone. The spraying pressure of the composite activation medium in the pre-spraying and renewal spraying zones is 0.45 MPa. The brushing component is a nylon roller brush, rotating at 500 rpm. The residence time of the pre-cleaned strip in the composite activation station is 35 seconds.

[0050] S4. The composite activated strip is conveyed to the rinsing station, where the surface of the composite activated strip is rinsed to remove residual composite activation medium and stripping material, resulting in rinsed strip. The rinsing station includes two rinsing units: the first rinsing unit uses process water spray rinsing, and the second rinsing unit uses deionized water spray rinsing.

[0051] S5. The rinsed strip steel is conveyed to the drying station, and the surface of the rinsed strip steel is dried to obtain the strip steel before coating. The drying process is carried out by air knife blowing and hot air drying in sequence. The hot air temperature is 130℃ and the drying time is 13s.

[0052] In this embodiment, the stubborn oxide layer, firmly attached contaminants, and interface residues on the strip surface before coating are more easily weakened and peeled off. The micro-abrasion effect of hard particles on the brushing area is more obvious, resulting in a more prominent micro-interlocking structure on the strip surface. The adhesion base of the subsequent coating is further enhanced, and the resulting strip surface is more inclined to be strengthened, activated, and roughened. It is suitable for strip pretreatment scenarios with high surface oxidation, strong contaminant adhesion, high requirements for adhesion of subsequent coatings, or the need to improve the peel resistance of the coating.

[0053] Example 4

[0054] Please see Figures 1-5 Based on Examples 1, 2 and 3, in order to verify the influence of different composite activation conditions on the surface condition of strip steel before coating, the same batch of cold-rolled strip steel was selected as the sample.

[0055] 1. Experimental setup

[0056] The sample size was 300mm×100mm×1.0mm, with 5 samples per group, and the average value of the test results was taken. Before treatment, the surface of the strip steel showed visible rolling oil film, a small amount of loose particles, and a slight oxide layer.

[0057] Testing revealed that the surface roughness Ra of the strip before treatment was 0.62 μm, and the residual oil content was 18.6 mg / m². 2 The oxidation residue area ratio is 23.5%, the water contact angle is 78°, and the coating cross-cut adhesion is level 2.

[0058] Among them, the surface roughness Ra was measured by a contact roughness meter, and three measuring points were taken for each sample along the rolling direction and perpendicular to the rolling direction. The amount of residual oil on the surface was measured by weighing after solvent extraction. The proportion of residual oxidation area was obtained by statistical analysis of surface microscopic images. The water contact angle was measured by a contact angle measuring instrument. The cross-cut adhesion of the coating was evaluated by the cross-cut method after completing the same coating conditions.

[0059] Before the adhesion test, the same epoxy primer was rolled onto the treated steel strip surface of each group, with the dry film thickness controlled at 20μm±2μm, and a cross-cut test was performed after curing under the same curing conditions.

[0060] This embodiment sets up three groups: Experiment A, Experiment B, and Experiment C. The source of the steel strip, sample size, batch of alkaline degreasing solution, rinsing process, testing methods, and coating test conditions are consistent across the three groups. The differences lie in the degreasing and cleaning temperature and time, the composition of the composite activation medium, the parameters of the hard microparticles, and the composite activation process conditions. Experiment A uses mild treatment conditions, Experiment B uses medium treatment conditions, and Experiment C uses intensive treatment conditions.

[0061] 2. Pre-cleaning treatment

[0062] The three groups of steel strips first enter the pre-cleaning station, where free oil and loose impurities on the surface are removed by spraying with alkaline degreasing solution. The alkaline degreasing solution used in all three groups is prepared in the same batch, with a pH value of 11.5 and an effective alkali mass fraction of 2.5%.

[0063] Experiment A used an alkaline degreasing solution at 48℃ for 10 seconds. Experiment B increased the temperature of the degreasing solution to 52℃ and extended the spraying time to 14 seconds. Experiment C further increased the temperature to 56℃ and sprayed for 18 seconds.

[0064] After pre-cleaning, the residual oil content on the surface of all three groups of strip steel decreased significantly. The residual oil content on the surface of the pre-cleaned strip steel in Experiment A decreased to 7.9 mg / m². 2 Experiment B decreased to 6.4 mg / m³ 2 Experimental C decreased to 5.2 mg / m³ 2 Meanwhile, the surface roughness Ra of the three strips were 0.64 μm, 0.65 μm and 0.66 μm, respectively, and the proportions of residual oxide area were 21.8%, 21.1% and 20.4%, respectively.

[0065] The above results indicate that the pre-cleaning stage is effective in removing free oil contaminants, and the degreasing effect is enhanced with increasing temperature and spraying time. However, this stage has little impact on the surface roughness of the strip, and the reduction in the residual oxide area is limited. This suggests that simple degreasing is insufficient to remove the oxide layer that is firmly bonded to the substrate, nor is it enough to form a micro-roughened structure suitable for coating adhesion. Therefore, in this process, pre-cleaning mainly serves to reduce the surface oil load and provide a stable contact interface for subsequent composite activation.

[0066] 3. Preparation of composite activation media

[0067] After pre-cleaning, three sets of composite activation media were prepared.

[0068] Experiment A used citric acid, nonionic surfactant, and polyacrylate to prepare an activation solution with a pH of 4.5. The mass fractions of citric acid, nonionic surfactant, and polyacrylate were 3%, 0.5%, and 0.3%, respectively. Subsequently, silica hard microparticles with an average particle size of 3 μm were added to make their mass fraction in the composite activation medium 1.5%, and the mixture was mechanically stirred for 12 min.

[0069] Experiment B used phosphoric acid, anionic surfactant, and hexametaphosphate instead, and the pH of the activation solution was adjusted to 3.5. The mass fractions of the three were 5%, 1%, and 0.7%, respectively. The hard microparticles were alumina with an average particle size of 5 μm, at a mass fraction of 3%, and mechanical stirring was performed for 15 min.

[0070] Experiment C used a stronger oxalic acid system, with a nonionic surfactant as the surface-active component and a polycarboxylate as the dispersion stabilizing component. The pH of the activation solution was 2.8. The mass fractions of oxalic acid, nonionic surfactant, and polycarboxylate were 7%, 1.5%, and 1%, respectively. The hard microparticles were silicon carbide with an average particle size of 7 μm, at a mass fraction of 4%, and mechanical stirring was performed for 18 min.

[0071] To investigate the dispersion state of the three media, 100 mL of the composite activation medium was allowed to stand for 30 min. The bottom deposition layer height was approximately 2.6 mm in Experiment A, approximately 1.8 mm in Experiment B, and approximately 2.1 mm in Experiment C. Experiment B had the lowest deposition layer height, indicating that the composite activation medium in Experiment B experienced less particle settling under standing conditions. After re-stirring, all three media recovered to a uniform suspension state, meeting the requirements for subsequent cyclic spraying and particle-carrying washing. Experiment C had a higher particle size and content of hard microparticles, but no significant agglomeration occurred under the action of polycarboxylate, meeting the requirements for subsequent cyclic spraying and particle-carrying washing.

[0072] Therefore, the composite activation medium is not a single acid solution or a single abrasive system. The acidic activation component weakens the bond between the oxide layer, oil residue, and the steel strip substrate; the surfactant component improves the spreading of the medium on the steel strip surface; the dispersion stabilizing component maintains the uniform distribution of hard particles; and the hard particles provide micro-abrasion during subsequent brushing. These components together form the basis for the subsequent synergistic treatment.

[0073] 4. Pre-spraying treatment

[0074] After entering the composite activation station, the three groups of pre-cleaned steel strips first passed through the pre-spraying zone. The spraying pressures of the composite activation medium in Experiments A, B, and C were 0.25 MPa, 0.35 MPa, and 0.45 MPa, respectively. After spraying, the composite activation medium formed a continuous medium film layer containing acidic activation liquid and hard particles on the surface of the steel strip.

[0075] Samples were taken immediately after pre-spraying for testing. The water contact angles on the strip surfaces of Experiments A, B, and C were 42°, 34°, and 29°, respectively. The decrease in water contact angle indicates improved spreadability of the composite activating medium on the strip surface.

[0076] The corresponding percentages of residual oxidation area decreased from 21.8%, 21.1%, and 20.4% to 18.6%, 15.9%, and 13.7%, respectively. At this point, the surface roughness Ra of the three strips were 0.67 μm, 0.69 μm, and 0.72 μm, respectively, showing only a slight increase compared to the pre-cleaning stage.

[0077] The results show that the main contribution of the pre-spraying stage is not to directly roughen the surface, but to enable the composite activation medium to fully wet the strip steel and enter the interface between the oxide layer, residual oil film and the substrate.

[0078] As the pH of the activation solution decreased and the spray pressure increased, the proportion of residual oxide area decreased from 21.8%, 21.1%, and 20.4% after pre-cleaning to 18.6%, 15.9%, and 13.7%, respectively, indicating that the composite activation medium had begun to weaken the bond between the oxide layer and the substrate. However, since the mechanical stripping effect of the brushing components had not yet been introduced at this stage, some of the weakened oxide layer and attached contaminants still remained on the surface. Therefore, pre-spraying plays a preliminary role in spreading, penetrating, and weakening the interface in the entire process, creating conditions for the next step of particle-carrying brushing.

[0079] 5. Particle-carrying brushing treatment

[0080] After pre-spraying, the strip continues into the particle-carrying brushing zone. In the particle-carrying brushing zone, a composite activation medium film continuously covers the surface of the strip, and nylon roller brushes drive hard particles to move relative to each other within the surface area that has been activated by the liquid.

[0081] The intensity of the particle-carrying brushing is increased in the order of A, B, and C: the nylon roller brush speeds are 300 rpm, 400 rpm, and 500 rpm, respectively, and the corresponding residence times are 15 s, 25 s, and 35 s, respectively.

[0082] After brushing with granules, the surface conditions of the three strips showed significant differences. In Experiment A, the surface roughness Ra increased to 0.82 μm, and the residual oil content decreased to 3.6 mg / m². 2 The proportion of oxidized residual area decreased to 10.5%, the Ra of Experiment B increased to 1.03 μm, and the residual oil content decreased to 2.1 mg / m³. 2 The proportion of oxidized residual area decreased to 5.3%, the Ra of experimental C increased to 1.27 μm, and the residual oil content decreased to 1.5 mg / m³. 2 The proportion of oxidized residual area decreased to 3.4%.

[0083] From the treatment results, Experiment A, due to its weaker acidity and smaller silica particle size, resulted in finer micro-undulations after brushing, improving surface cleanliness, but the degree of roughening was relatively limited. In Experiment B, the activation effect of phosphoric acid on the oxide layer interface combined well with the micro-abrasion effect of alumina particles, showing a relatively balanced improvement in residual oil, oxide residue area, and roughness. In Experiment C, due to the stronger acidity of the oxalic acid system and the larger particle size of silicon carbide particles, the micro-abrasion effect was further enhanced at higher rotation speeds and longer residence times, resulting in more thorough removal of firmly bonded oxide layers and contaminants, and a more pronounced micro-uneven structure on the resulting surface.

[0084] To further verify the synergistic effect, two process observation samples were set up under Experiment B conditions. The spray pressure, roller brush speed, residence time, rinsing and drying conditions of the two process observation samples were kept consistent with those of Experiment B, and the only difference was whether the composite activation medium contained acidic activation components or hard particles.

[0085] The first group was brushed with Experiment B activation solution, which did not contain alumina hard particles. The activation solution still contained phosphoric acid, anionic surfactant, and hexametaphosphate. After treatment, the surface roughness Ra of the strip was 0.78 μm, and the residual oil content was 3.8 mg / m. 2 The residual oxidation area ratio was 11.6%. The second group underwent brushing with a dispersion containing alumina particles but no phosphoric acid. The dispersion retained anionic surfactants, hexametaphosphate, and hard alumina particles. After treatment, the Ra was 0.91 μm, and the residual oil content was 4.2 mg / m³. 2 The percentage of oxidized residual area was 13.4%.

[0086] In comparison, under the complete experimental condition B, the surface Ra of the strip reached 1.03 μm, and the residual oil content decreased to 2.1 mg / m². 2 The proportion of oxidized residue area decreased to 5.3%. The above comparison shows that although chemical activation alone can reduce the bonding strength between dirt and substrate, its peeling ability is insufficient. Although particle scrubbing alone can improve roughness, it is not sufficient to remove oil and oxide layer interfaces.

[0087] It can be seen that the acidic activation solution can first reduce the bonding strength between the oxide layer and residual oil and the substrate. The hard particles, driven by the roller brush, perform micro-erosion and peeling on the same activated area. After the two work together, the residual oil and the proportion of oxide residue area in Experiment B are lower than those of the two process observation samples. At the same time, Ra is higher than that of the observation sample that was only washed with activation solution, thus achieving simultaneous improvement in cleanliness and surface micro-roughening.

[0088] 6. Update spray treatment

[0089] After the grain-carrying washing is completed, the strip steel enters the renewal spraying zone.

[0090] Experiments A, B, and C continued to use spray pressures of 0.25 MPa, 0.35 MPa, and 0.45 MPa, respectively, to spray the composite activation medium onto the brushed surface. The replacement spraying served two purposes: firstly, to replenish the activation liquid and hard particles; and secondly, to promptly remove oil, oxide debris, flaking material, and expired medium generated during the brushing process from the steel strip surface.

[0091] After the spraying was updated, the residual oil content on the surface of the strip in Experiment A increased from 3.6 mg / m² after particle-carrying and brushing. 2 Reduced to 2.9 mg / m³ 2 The proportion of oxidized residual area decreased from 10.5% to 8.4%, Ra was 0.86 μm, and the residual oil content in Experiment B decreased from 2.1 mg / m² to 1.7 mg / m². 2 The percentage of residual oxidized area decreased from 5.3% to 4.1%, Ra was 1.08 μm, and the residual oil content in experiment C decreased from 1.5 mg / m². 2 Reduced to 1.2 mg / m³ 2 The proportion of oxidized residual area decreased from 3.4% to 2.7%, and Ra was 1.31 μm.

[0092] To determine the impact of renewal spraying on the cleaning effect, a control group was established by canceling renewal spraying under Experiment B condition. After canceling renewal spraying, the residual oil content on the strip surface was 2.6 mg / m². 2 The oxidation residue area was 6.8%, and microscopic observation of the surface revealed fine residues even in localized micro-depressions. When the oil was retained for renewal injection, the residual oil content was 1.7 mg / m³. 2 The area of ​​oxidized residue was 4.1%, and the surface residue was reduced under microscopic observation.

[0093] The comparison shows that the role of the renewal spray is not limited to replenishing the composite activation medium, but also in promptly removing the sludge formed by brushing from the treated surface. Without this step, the activated and sludge can easily remain in brush marks or micro-depressions, weakening the treatment effect of the previous stage.

[0094] Therefore, within the same composite activation station, pre-spraying first allows the activation liquid to enter the interface between the oxide layer and residual oil, and particle-carrying brushing further completes micro-erosion and stripping. Renewal spraying then discharges the stripped material and replenishes the effective medium, so that the residual oil content and the ratio of oxide residual area continue to decrease after particle-carrying brushing.

[0095] 7. Rinsing treatment

[0096] After the composite activation is completed, the three strips are sequentially rinsed with process water and then with deionized water to remove residual composite activation medium and stripping material from the surface. The spray pressure for both stages of rinsing is 0.20 MPa, the first stage of process water rinsing time is 8 seconds, the second stage of deionized water rinsing time is 8 seconds, and the rinsing water temperature is room temperature.

[0097] After rinsing, no obvious treatment solution residue was observed on the surface of any of the three strips. Testing showed that the residual electrical conductivity on the strip surface was 18 μS / cm in Experiment A, 13 μS / cm in Experiment B, and 15 μS / cm in Experiment C.

[0098] Experiment A had a lower treatment intensity and produced less sloughed material in the initial stage, resulting in controllable residual levels after rinsing. Experiment B effectively removed sloughed material during the renewal spraying stage, leading to the lowest residual conductivity value after rinsing. Experiment C exhibited stronger activation and micro-abrasion effects, resulting in more pronounced surface micro-unevenness. Its residual conductivity value after rinsing was slightly higher than Experiment B, but still lower than Experiment A. The rinsing effect depends not only on the rinsing process itself but also on the effectiveness of the initial renewal spraying and changes in surface morphology.

[0099] 8. Comparison of drying and final surface properties

[0100] After rinsing, all three groups of steel strips were first purged with an air knife for 5 seconds at a pressure of 0.30 MPa, and then dried with hot air. The hot air temperature for Experiment A was 110℃, and the drying time was 7 seconds; for Experiment B, the hot air temperature was 120℃, and the drying time was 10 seconds; and for Experiment C, the hot air temperature was 130℃, and the drying time was 13 seconds. After drying, no continuous watermarks were observed on the surface of any of the three groups of steel strips.

[0101] Three groups of pre-coated steel strips were coated under the same coating and curing conditions, and then subjected to cross-cut adhesion tests. The final test results showed that the surface roughness Ra of the pre-coated steel strip obtained in Experiment A was 0.86 μm, and the residual oil content was 2.9 mg / m². 2 The oxidation residue area ratio was 8.4%, the water contact angle was 38°, and the coating cross-cut adhesion was grade 1. Experiment A showed that the steel strip surface formed relatively fine micro-undulations, which is suitable for scenarios with light initial contamination or where subsequent coatings should not use substrates with excessively high roughness.

[0102] The Ra of the strip before coating obtained in Experiment B was 1.08 μm, and the residual oil content on the surface was 1.7 mg / m². 2 The oxidation residue area ratio was 4.1%, the water contact angle was 31°, and the coating cross-cut adhesion was grade 0. Experiment B balanced cleanliness and roughness improvement, with less surface residue and moderate micro-roughness, making it a suitable preferred condition for pretreatment before conventional strip coating.

[0103] The Ra of the strip before coating obtained in Experiment C was 1.31 μm, and the residual oil content on the surface was 1.2 mg / m². 2 The oxidation residue area ratio was 2.7%, the water contact angle was 27°, and the coating cross-cut adhesion was grade 0. Experiment C showed more thorough removal of stubborn oxide layers and firmly attached contaminants, and the resulting micro-interlocking structure was more obvious. It is suitable for strip steel treatment with a high degree of surface oxidation or where high adhesion strength of subsequent coatings is required.

[0104] As can be seen from the above step-by-step comparison, pre-cleaning can reduce the oil load on the strip surface, but its contribution to oxidation residue and surface roughening is limited. After entering the composite activation stage, the acidic activation component first weakens the interfacial bonding between the oxide layer and the attached dirt and the substrate, the surface active component improves the wetting and spreading ability of the composite activation medium on the strip surface, the dispersing and stabilizing component ensures that the hard particles are effectively distributed in the circulation system, and the hard particles perform micro-erosion and peeling on the same activated surface area under the drive of the nylon roller brush, and the renewal spray removes the peeled material, residual oil and failed medium in a timely manner.

[0105] The results from the three groups show that Experiment A exhibited mild cleaning and slight roughening, Experiment B showed a balanced improvement in both cleanliness and roughness, and Experiment C showed enhanced activation and a higher degree of surface roughening. These results indicate that degreasing alone primarily reduces surface oil load, while chemical activation or particle brushing alone is insufficient to simultaneously achieve oxide layer removal and surface micro-roughening. By employing a composite activation medium, particle-carrying brushing, and continuous re-spraying treatment, the residual oil content, oxide residue area ratio, and surface roughness of the strip surface were simultaneously improved, achieving a synergistic improvement in cleanliness and roughness before coating.

[0106] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A composite activation method for synergistically improving the surface roughness and cleanliness of steel strips before coating, characterized in that, include: S1. The strip steel to be processed is conveyed to the pre-cleaning station, and the surface of the strip steel to be processed is degreased and cleaned to obtain pre-cleaned strip steel; S2. The acidic activating component, the surface-active component, and the dispersion stabilizing component are added to a liquid medium and mixed to obtain an activated solution; Hard microparticles are added to the activation solution for dispersion to obtain a composite activation medium; S3. The pre-cleaned strip is conveyed to the composite activation station, which is sequentially configured with a pre-spraying zone, a particle-carrying brushing zone, and a renewal spraying zone along the conveying direction of the pre-cleaned strip. In the pre-spraying zone, the composite activation medium is sprayed onto the surface of the pre-cleaned strip, forming a medium film layer containing the activation liquid and the hard particles on the surface of the pre-cleaned strip. In the particle-carrying brushing zone, while the medium film layer continuously covers the surface of the pre-cleaned strip, a brushing component is used to brush the surface of the pre-cleaned strip. The activation liquid acts on the oxide layer and the interface between the adhering dirt and the substrate on the pre-cleaned strip surface. The hard particles, driven by the brushing component, perform micro-abrasion and peeling treatment on the same surface area treated by the activation liquid. In the renewal spraying zone, the composite activation medium is continued to be sprayed onto the strip surface treated by the particle-carrying brushing zone, renewing the medium film layer on the strip surface and removing the peeling material and residual medium formed during the brushing process. The redeposition of the peeling material in the micro-depressions on the surface formed by micro-abrasion is inhibited, resulting in a composite activated strip. S4. The composite activated strip steel is conveyed to the rinsing station, and the surface of the composite activated strip steel is rinsed to obtain rinsed strip steel. S5. The rinsed strip is conveyed to the drying station and the surface of the rinsed strip is dried to obtain strip before coating.

2. The composite activation method for synergistically improving surface roughness and cleanliness of steel strip before coating according to claim 1, characterized in that: The pre-cleaning station uses an alkaline degreasing solution for spray cleaning, with the temperature of the alkaline degreasing solution being 45℃-60℃; the spraying treatment time is 8s-20s.

3. The composite activation method for synergistically improving surface roughness and cleanliness of steel strip before coating according to claim 1, characterized in that: The acidic activating component is selected from one of phosphoric acid, citric acid and oxalic acid; the surfactant component is selected from one of nonionic surfactant and anionic surfactant; and the dispersion stabilizing component is selected from one of polyacrylate, hexametaphosphate and polycarboxylate.

4. The composite activation method for synergistically improving surface roughness and cleanliness of steel strip before coating, as described in claim 3, is characterized in that: The liquid medium is deionized water, and the pH value of the activation solution is 1.5-5.

5.

5. The composite activation method for synergistically improving surface roughness and cleanliness of steel strip before coating according to claim 3, characterized in that: The acidic activating component has a mass fraction of 1%-10% in the activating solution, the surface active component has a mass fraction of 0.1%-2% in the activating solution, and the dispersion stabilizing component has a mass fraction of 0.05%-1.5% in the activating solution.

6. The composite activation method for synergistically improving surface roughness and cleanliness of steel strip before coating according to claim 1, characterized in that: The hard microparticles are selected from one of alumina, silicon carbide, silicon dioxide and cerium oxide, the average particle size of the hard microparticles is 1μm-10μm, and the mass fraction of the hard microparticles in the composite activation medium is 0.5%-5%.

7. The composite activation method for synergistically improving surface roughness and cleanliness of steel strip before coating according to claim 1, characterized in that: The dispersion is carried out by mechanical stirring, and the dispersion time is 10 min-20 min; the composite activation medium is circulated and transported between the pre-spraying zone, the particle-carrying brushing zone and the renewal spraying zone.

8. The composite activation method for synergistically improving surface roughness and cleanliness of steel strip before coating according to claim 1, characterized in that: The injection pressure of the composite activation medium in the pre-injection zone and the renewal injection zone is 0.2MPa-0.5MPa.

9. The composite activation method for synergistically improving surface roughness and cleanliness of steel strip before coating according to claim 1, characterized in that: The brushing component is a nylon roller brush, and the rotation speed of the nylon roller brush is 200rpm-600rpm; the residence time of the pre-cleaned strip steel in the composite activation station is 10s-40s.

10. The composite activation method for synergistically improving surface roughness and cleanliness of steel strip before coating according to claim 1, characterized in that: The rinsing station includes two rinsing units. The first rinsing unit uses process water spray rinsing, and the second rinsing unit uses deionized water spray rinsing. The drying process is carried out by air knife blowing and hot air drying in sequence. The hot air temperature is 100℃-140℃, and the drying time is 5s-15s.

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