A method of in situ filling of pores in a tungsten carbide coating on a surface of a corrugating roll

Abstract

The application discloses a method for filling pores of a tungsten carbide coating on a surface of a corrugated roller in situ, and comprises the following steps: S1, placing the corrugated roller sprayed with the tungsten carbide coating in a tetrabutyl titanate / ethanol solution for immersion, and in-situ converting and filling most of the pores in the coating in the pores of the coating; S2, placing the corrugated roller in an alkaline electrolyte for electrolytic polishing, so as to uniformly process a surface morphology of the tungsten carbide coating and generate hydroxyl reaction sites on the surface; S3, placing the corrugated roller after S2 in a KH570 ethanol solution, and forming a hydrogen bond or a covalent bond between one end of a silane coupling agent and titanium dioxide; and S4, scraping an acrylic resin coating on the surface of the corrugated roller after S3. The application constructs a gradient interface structure of an inorganic pore-filling phase-molecular bridge-organic functional top layer in the pores of the tungsten carbide coating on the corrugated roller, and solves the problems of corrosion failure, fatigue peeling and pulp adhesion caused by the coating pores.

Description

Technical Field

[0001] This invention relates to the field of corrugated roll manufacturing technology, and in particular to a method for in-situ filling of the pores in the tungsten carbide coating on the surface of a corrugated roll. Background Technology

[0002] As a core forming component in corrugated cardboard production lines, the surface quality of corrugated rolls directly determines the forming accuracy, production efficiency, and energy consumption of the cardboard. Under harsh conditions of high speed, high pressure, and continuous operation, the tooth surface of corrugated rolls is subjected to severe abrasive wear from paper fibers, cyclic mechanical stress, and erosion from moisture and chemicals during the pulping process. To significantly improve its wear resistance and service life, modern high-end corrugated roll manufacturing commonly employs the preparation of tungsten carbide (WC)-based hard coatings on the surface of alloy steel roll bodies, such as high-density WC-Co or WC-Ni-based coatings formed through technologies like supersonic flame spraying.

[0003] However, even with current advanced technology, high-quality tungsten carbide coatings still struggle to completely eliminate micron- and submicron-sized pores in their microstructure. During high-pressure forming, hard impurities in the cardboard (such as sand particles and mineral fillers) and reinforcing fibers impact and scratch the toothed surfaces. Pores in the coating, especially when they form a micro-network within the coating or extend into the matrix, become weak points in the material. Under cyclic stress, microcracks easily form and propagate at the pore edges, causing the coating material to peel off prematurely in granular form, forming macroscopic abrasive particles. This not only accelerates the wear of the coating itself and the abrasive components but can also scratch the cardboard surface, affecting the product's appearance and strength. Furthermore, surface imperfections caused by pores exacerbate paper fiber adhesion, requiring frequent shutdowns for cleaning and disrupting continuous production.

[0004] The production environment for corrugated cardboard is characterized by high humidity, and the pulp itself is weakly acidic or alkaline, potentially containing corrosive components such as chloride ions. The interconnected pores in the coating provide a "fast track" for these corrosive media to reach the substrate interface. The corrosion products of the substrate material, such as iron oxides, expand in volume, generating enormous internal stress at the coating / substrate interface. This ultimately leads to large-scale peeling of the coating in the form of "bubbling" or flakes, causing catastrophic failure far exceeding simple uniform wear.

[0005] The presence of porosity directly reduces the effective cross-sectional area of ​​the coating to withstand contact stress, thus lowering its macroscopic hardness and compressive strength. Porosity in stress concentration areas such as the tooth root can easily become fatigue crack initiation points, potentially leading to tooth tip chipping. Simultaneously, porosity at the interface significantly weakens the mechanical bond between the coating and the roller substrate, dramatically increasing the risk of coating detachment under complex alternating loads. Summary of the Invention

[0006] The purpose of this invention is to provide a method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roll. This invention solves the problems of corrosion failure, fatigue peeling and pulp adhesion caused by coating pores by constructing a gradient interface structure of inorganic pore-filling phase-molecular bridge-organic functional top layer in the pores of the tungsten carbide coating of the corrugated roll.

[0007] To solve this technical problem, the technical solution of the present invention is: a method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roll, comprising the following steps: S1. The corrugated roller coated with tungsten carbide is immersed in a tetrabutyl titanate / ethanol solution, so that the tetrabutyl titanate penetrates into the coating pores and undergoes hydrolysis and condensation during the drying process, transforming in situ into titanium dioxide precursor and / or nano titanium dioxide in the coating pores to fill most of the pores in the coating. S2. Connect the corrugated roller that has passed through S1 to the positive terminal of the power supply as the anode of electrolytic processing, and the platinum carbon electrode as the cathode. Place the corrugated roller in an alkaline electrolyte for electrolytic polishing to uniformly shape the surface morphology of the tungsten carbide coating and generate hydroxyl reaction sites on the surface. S3. Place the corrugated roller that has passed through S2 into a KH570 ethanol solution. KH570 condenses on the coating surface, and one end of the silane coupling agent forms a hydrogen bond or a covalent bond with titanium dioxide. S4. Apply a fluorinated acrylic resin coating to the surface of the corrugated roll that has passed through S3. The fluorinated acrylic resin forms a strong chemical bond with the titanium dioxide and tungsten carbide coating in the pores through KH570 molecular bridges. The coating is then heated and cured, and naturally cooled and air-dried to obtain an interface structure of TiO2 pore-filling phase - KH570 molecular bridge - fluorinated acrylic resin top layer for filling the pores of the tungsten carbide coating of the target corrugated roll.

[0008] In preferred step S1, the volume ratio of tetrabutyl titanate to ethanol is 1:(3-5), the immersion temperature is 70°C, the immersion time is 2h, and then it is dried at 120°C for 3h.

[0009] The preferred alkaline electrolyte in step S2 comprises the following substances by mass fraction: 0.5% sodium nitrate; 0.4% sodium chloride; 0.5%–3% complexing agent; 1%–5% disodium hydrogen phosphate; 5%–15% glycerol and ethylene glycol combined; 0.1%–1% sodium gluconate; balance water; The pH was adjusted to 12-13 using sodium hydroxide, and the electrolysis temperature was controlled at 30-50℃.

[0010] The preferred KH570 mass fraction in the KH570 ethanol solution in step S3 is 3% to 5%.

[0011] In this invention, the processing temperature is room temperature, the processing time is 30 min, and then drying is carried out at 80°C for 1 h.

[0012] The preferred step S4 uses a water-based emulsion with a solid content of 30% to 50% and a viscosity of 2000 to 5000 mPa·s, containing the anchoring agent DOUBLEMER® 278-X25 and a silane coupling agent. The amount of anchoring agent added is 3% to 10% of the solid mass of fluorinated acrylic resin; The amount of KH570 added is 1% to 5% of the solid mass of the fluorinated acrylic resin; The glass transition temperature of the fluorinated acrylic resin is not lower than 80°C.

[0013] In step S4, the fluorinated acrylic resin coating is preferably applied by a scraping method. The curing process for fluorinated acrylic resin coatings includes the following steps: S41. Let stand at room temperature for 10-15 minutes until the surface is dry and leveled. S42, cure at 40-50℃ for 20-30 min; S43. Heat to 60-70℃ and hold for 45 minutes; S44. Allow to cool naturally at room temperature and air dry for 24 hours.

[0014] Preferably, the tungsten carbide coating is a cobalt-based tungsten carbide coating; The cobalt-based tungsten carbide coating was prepared using supersonic flame spraying technology with an oxygen pressure of 0.56 MPa and a flow rate of 160 L / min, a propane pressure of 0.48 MPa and a flow rate of 17 L / min, a spraying distance of 275 mm, and a coating thickness of 250 μm.

[0015] This invention uses a cobalt-based tungsten carbide coating as the hard layer on the surface of the corrugated roll. The cobalt-based tungsten carbide coating has a Vickers hardness (HV) of 1200–1600 and a fracture toughness (K). IC 8–12 MPa·m 1 / 2 It can effectively resist abrasive wear and fatigue damage of corrugated rollers under high-speed and high-pressure conditions. At the same time, the microporous structure with a pore size of 0.5-3μm formed by HVOF spraying of the cobalt-based tungsten carbide coating is suitable for deep penetration of tetrabutyl titanate, and the hydroxyl groups exposed on the coating surface after electrolytic polishing have good chemical compatibility with KH-570, providing an ideal microstructure basis for building a robust gradient interface.

[0016] Preferably, the spraying powder of the cobalt-based tungsten carbide coating comprises the following substances in parts by mass: Co powder, 1-6 parts; 0.5–2 parts of Cr3C2 powder; Vitamin C powder 0.5–2 parts; 90.0–94.5 parts of tungsten carbide powder.

[0017] The preferred method for preparing cobalt-based tungsten carbide includes the following steps: S11. After uniformly mixing Co powder, Cr3C2 powder and VC, place them with tungsten carbide powder in a ball mill for spherical mixing. S12. Place the powder mixed in step S11 into a graphite negative mold and pre-press it using a hydraulic press. The pre-pressing pressure is 5-20 MPa and the holding time is 5 min. S13. Place the assembled graphite mold in the spark plasma sintering system, set the axial pressure to 0-50 MPa, evacuate to below 5 Pa, and sinter by powering on; set the heating rate to 5℃-30℃ / min, the sintering temperature to 1250℃-1450℃, and the holding time to 5-15 min. S14. The sample is removed using a hydraulic press, and the graphite on the sample surface is removed by grinding to obtain a cobalt-based tungsten carbide composite cemented carbide material.

[0018] The preferred process parameters for immersing the corrugated roller in the tetrabutyl titanate / ethanol solution in step S1 are as follows: Immersion temperature: 65℃ to 75℃; Soaking time: 2 hours; Dry at 120℃ for 3 hours.

[0019] By adopting the above technical solution, the beneficial effects of the present invention are: The micron- and submicron-sized pores commonly found in the tungsten carbide coating of corrugated rolls easily become stress concentration points during high-pressure forming, triggering microcrack propagation. In wet pulp environments, they also act as channels for corrosive media to reach the substrate directly. This invention first employs a tetrabutyl titanate (TTIP) / ethanol solution to impregnate the coating. The TTIP molecular size is suitable for penetrating the coating pores. During drying at 120°C, TTIP undergoes a hydrolysis-condensation reaction, generating nano-TiO2 particles in situ within the pores, effectively filling most of the pores and reducing the coating porosity from 3.6%–4.7% to 0.5%–2%. This step eliminates the role of pores as crack initiation points and corrosion pathways. Simultaneously, the thermal expansion coefficient of TiO2 matches well with the WC coating, providing a stable inorganic substrate for subsequent interface construction. The coating surface after pore filling may exhibit uneven deposition and roughness. This invention employs an alkaline electrolyte (pH≈12.5) containing complexing agents and brighteners for electrolytic polishing, selectively dissolving and passivating micro-protrusions on the coating surface to obtain a uniform and smooth morphology. Simultaneously, a large number of hydroxyl groups are generated on the TiO2 particles and tungsten carbide coating surface. These hydroxyl groups provide reactive sites for the subsequent chemical bonding of silane coupling agents, effectively solving the secondary problem of "local stress concentration caused by surface roughness after pore filling." In step S3, KH570 (γ-methacryloyloxypropyltrimethoxysilane) is used as a bifunctional molecular bridge: the trimethoxysilane end of KH570 undergoes hydrolytic condensation with the hydroxyl groups of TiO2 on the coating surface and within the pores, forming covalent bonds on the Si-O-Ti / Si-O- coating surface. Simultaneously, KH570... The acryloyl group at the other end of the molecule retains double bond activity, allowing it to copolymerize and crosslink with subsequent fluorinated acrylic resins. This molecular bridge construction process firmly connects the rigid WC-TiO2 composite coating to the flexible organic resin through chemical bonds, overcoming the problems of large differences in thermal expansion coefficients between traditional rigid coatings and organic sealing agents, poor interfacial adhesion, and easy peeling under thermal cycling and mechanical impact. A fluorinated acrylic resin emulsion is coated onto the KH570 molecular bridge layer, controlling the dry film thickness to 0.10 mm, which allows penetration of residual micropores and the formation of a continuous functional layer on the surface. Through a mild curing process of 40–50℃ pre-curing and 60–70℃ main curing, the crosslinking monomers in the resin react with the acryloyl groups of KH570 to form a three-dimensional network. The fluorinated side chains accumulate outward, generating low surface energy and a water contact angle greater than 100°. This organic top layer solves the problem of pulp fiber adhesion and provides flexible cushioning to alleviate contact stress at the tooth apex. The present invention obtains a nano-TiO2-KH570 molecular bridge-fluorinated acrylic resin top layer that fills the voids in the tungsten carbide coating on the surface of the corrugated roll WC coating through steps S1 to S4. The resulting composite film structure coating has a 3 to 5 times longer salt spray resistance time and a 40% to 60% reduction in wear. Under alternating loads of 140 to 200°C, there is no interface peeling phenomenon, which effectively solves the comprehensive failure problem caused by the porous structure of the corrugated roll coating. Detailed Implementation

[0020] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0021] Example 1

[0022] This embodiment discloses a method for in-situ filling of pores in the tungsten carbide coating on the surface of a corrugated roller. In this embodiment, a 48CrMo alloy steel corrugated roller is selected as the substrate, and a cobalt-based tungsten carbide coating is sprayed onto the surface using supersonic flame spraying technology.

[0023] In this embodiment, the composition (parts by weight) of the cobalt-based tungsten carbide coating spray powder is as follows: 4 parts Co powder, 1 part Cr3C2 powder, 1 part VC powder, and 94 parts tungsten carbide powder.

[0024] In this embodiment, the tungsten carbide spraying process parameters are: oxygen pressure 0.56 MPa, flow rate 160 L / min; propane pressure 0.48 MPa, flow rate 17 L / min; spraying distance 275 mm, resulting in a tungsten carbide coating with a thickness of 250 μm. The specific method includes the following steps: S1. The corrugated roller coated with tungsten carbide is immersed in a tetrabutyl titanate / ethanol solution, so that the tetrabutyl titanate penetrates into the coating pores and undergoes hydrolysis and condensation during the drying process, transforming in situ into titanium dioxide precursor and / or nano titanium dioxide in the coating pores to fill most of the pores in the coating. The volume ratio of tetrabutyl titanate to ethanol in the tetrabutyl titanate / ethanol solution is 1:4. The corrugated roller with tungsten carbide coating is immersed in the solution at 70°C for 2 hours, and then removed and dried in an oven at 120°C for 3 hours.

[0025] S2. Connect the corrugated roller that has passed through S1 to the positive terminal of the power supply as the anode of electrolytic processing, and the platinum carbon electrode as the cathode. Place the corrugated roller in an alkaline electrolyte for electrolytic polishing to uniformly shape the surface morphology of the tungsten carbide coating and generate hydroxyl reaction sites on the surface. Prepare the electrolyte (mass fraction): sodium nitrate 0.5%, sodium chloride 0.4%, EDTA 1%, disodium hydrogen phosphate 2%, glycerol 5%, ethylene glycol 5%, sodium gluconate 0.5%, with the remainder being water. Adjust the pH to 12.5 with NaOH.

[0026] The corrugated roller passing through S1 is connected to the positive and negative electrodes, and electrolyzed at 40℃ for 15 minutes, with the current density controlled at 5-10 A / dm³. 2 .

[0027] S3. Place the corrugated roller that has passed through S2 into a KH570 ethanol solution. KH570 condenses on the coating surface, and one end of the silane coupling agent forms a hydrogen bond or covalent bond with titanium dioxide. Immerse it in the solution at room temperature for 30 min, and then dry it at 80℃ for 1 h. The mass fraction of KH570 in the KH570 ethanol solution in step S3 is 4%.

[0028] S4. Apply a fluorinated acrylic resin coating to the surface of the corrugated roll that has passed through S3. The fluorinated acrylic resin forms a strong chemical bond with the titanium dioxide and tungsten carbide coating in the pores through KH570 molecular bridges. The coating is then heated and cured, and naturally cooled and air-dried to obtain an interface structure of TiO2 pore-filling phase - KH570 molecular bridge - fluorinated acrylic resin top layer for filling the pores of the tungsten carbide coating of the target corrugated roll.

[0029] In step S4, the fluorinated acrylic resin is applied in solution form via scraping. The solution has a solid content of 40% and a viscosity of 3500 mPa·s. The curing process is as follows: S41, let stand at room temperature for 12 min; S42, 45℃ / 25 min; S43, 65℃ / 45 min; S44, air dry at room temperature for 24 hours.

[0030] Example 2

[0031] The only difference between this embodiment and Embodiment 1 is that: In step S1, the volume ratio of tetrabutyl titanate to ethanol in the tetrabutyl titanate / ethanol solution is 1:2.

[0032] Example 3

[0033] The only difference between this embodiment and Embodiment 1 is that: In step S1, the volume ratio of tetrabutyl titanate to ethanol in the tetrabutyl titanate / ethanol solution is 1:3.

[0034] Example 4

[0035] The only difference between this embodiment and Embodiment 1 is that: In step S1, the volume ratio of tetrabutyl titanate to ethanol in the tetrabutyl titanate / ethanol solution is 1:5.

[0036] Example 5

[0037] The only difference between this embodiment and Embodiment 1 is that: In step S1, the volume ratio of tetrabutyl titanate to ethanol in the tetrabutyl titanate / ethanol solution is 1:8.

[0038] Example 6

[0039] The only difference between this embodiment and Embodiment 1 is that: The acrylic resin used in step S4 is an acrylic resin (non-fluorinated).

[0040] Comparative Example 1 This comparative example discloses a method for in-situ filling of pores in a tungsten carbide coating on the surface of a corrugated roll, comprising the following steps: S1. The corrugated roller prepared in Example 1 is connected to the positive terminal of the power supply as the anode of electrolytic processing, and the platinum carbon electrode is the cathode. The corrugated roller is placed in an alkaline electrolyte for electrolytic polishing to uniformly shape the surface morphology of the tungsten carbide coating and generate hydroxyl reaction sites on the surface. Prepare the electrolyte (mass fraction): sodium nitrate 0.5%, sodium chloride 0.4%, EDTA 1%, disodium hydrogen phosphate 2%, glycerol 5%, ethylene glycol 5%, sodium gluconate 0.5%, with the remainder being water. Adjust the pH to 12.5 with NaOH.

[0041] The corrugated roller passing through S1 is connected to the positive and negative electrodes, and electrolyzed at 40°C for 15 min with a current density of 5–10 A / dm³. 2 .

[0042] S2. Place the corrugated roller that has passed through S1 into a KH570 ethanol solution. KH570 condenses on the coating surface, and one end of the silane coupling agent forms a hydrogen bond or a covalent bond with titanium dioxide. Immerse it in the solution at room temperature for 30 min, and then dry it at 80°C for 1 h. The mass fraction of KH570 in the KH570 ethanol solution in step S2 is 4%.

[0043] S3. Apply a fluorinated acrylic resin coating to the surface of the corrugated roll that has passed through S2. The fluorinated acrylic resin forms a strong chemical bond with the titanium dioxide and tungsten carbide coating in the pores through KH570 molecular bridges. The coating is then heated and cured, and naturally cooled and air-dried to obtain the interface structure of KH570 molecular bridges-fluorinated acrylic resin top layer used to fill the pores of the tungsten carbide coating of the target corrugated roll.

[0044] In step S4, the fluorinated acrylic resin is applied in solution form via scraping. The solution has a solid content of 40% and a viscosity of 3500 mPa·s. The curing process is as follows: S41, let stand at room temperature for 12 min; S42, 45℃ / 25 min; S43, 65℃ / 45 min; S44, air dry at room temperature for 24 hours.

[0045] Comparative Example 2 This comparative example discloses a method for in-situ filling of pores in a tungsten carbide coating on the surface of a corrugated roll, the specific method including the following steps: S1. The corrugated roller with tungsten carbide coating prepared in Example 1 is immersed in tetrabutyl titanate / ethanol solution, so that tetrabutyl titanate penetrates into the coating pores and undergoes hydrolysis and condensation during the drying process, and is converted in situ into titanium dioxide precursor and / or nano titanium dioxide in the coating pores to fill most of the pores in the coating. The volume ratio of tetrabutyl titanate to ethanol in the tetrabutyl titanate / ethanol solution is 1:4. The corrugated roller with tungsten carbide coating is immersed in the solution at 70°C for 2 hours, and then removed and dried in an oven at 120°C for 3 hours.

[0046] S2. Connect the corrugated roller that has passed through S1 to the positive terminal of the power supply as the anode of electrolytic processing, and the platinum carbon electrode as the cathode. Place the corrugated roller in an alkaline electrolyte for electrolytic polishing to uniformly shape the surface morphology of the tungsten carbide coating and generate hydroxyl reaction sites on the surface. Prepare the electrolyte (mass fraction): sodium nitrate 0.5%, sodium chloride 0.4%, EDTA 1%, disodium hydrogen phosphate 2%, glycerol 5%, ethylene glycol 5%, sodium gluconate 0.5%, with the remainder being water. Adjust the pH to 12.5 with NaOH.

[0047] The corrugated roller passing through S1 is connected to the positive and negative electrodes, and electrolyzed at 40℃ for 15 minutes, with the current density controlled at 5-10 A / dm³. 2 .

[0048] S3. Apply a coating of fluorinated acrylic resin to the surface of the corrugated roll that has passed through S2, heat and cure, and allow to cool and air dry naturally to obtain an interface structure of TiO2 pore-filling phase-fluorinated acrylic resin top layer for filling the pores of the tungsten carbide coating of the target corrugated roll.

[0049] In step S4, the fluorinated acrylic resin is applied in solution form via scraping. The solution has a solid content of 40% and a viscosity of 3500 mPa·s. The curing process is as follows: S41, let stand at room temperature for 12 min; S42, 45℃ / 25 min; S43, 65℃ / 45 min; S44, air dry at room temperature for 24 hours.

[0050] Performance tests were conducted on the corrugated rolls obtained in Examples 1 to 6 and Comparative Examples 1 to 2, respectively. The specific test data are shown in Table 1.

[0051] Table 1 Performance indicators of corrugated tungsten carbide coatings obtained in Examples 1 to 6 and Comparative Examples 1 and 2

[0052] The specific test methods and standard conditions in Table 1 are as follows: Porosity: GB / T 3246-2018, 20 fields of view were randomly selected, each field of view having an area of ​​1 mm². 2 The image was analyzed using ImageJ software.

[0053] Water contact angle: GB / T14286-2018, contact angle measuring instrument, room temperature 25℃, pure water droplet volume 2 μL, static drop method, average value of 5 parallel points.

[0054] Oil contact angle: GB / T14286-2018, contact angle measuring instrument, same as water contact angle, use xylene or mineral oil instead of pure water.

[0055] Cross-cut adhesion: GB / T9286-1998, 1 mm spacing cross-cut knife, cut 100 grids, 3M tape peel off, observe for 6 seconds and evaluate.

[0056] Salt spray resistance: GB / T1771-2007, 5% NaCl solution, pH 6.5~7.2, 35℃, continuous spraying until corrosion area is greater than 5%.

[0057] Wear volume: GB / T12718-2007, load 200N, rotation speed 300r / min, SiC sandpaper, test time 30 min, volume loss is calculated as mass loss / density.

[0058] Pulp adhesion: The testing steps are as follows: For sample pretreatment, the coated sample was placed in an environment of 25℃ and 50% RH for 24 h to equilibrate. The surface was wiped with a lint-free cloth and isopropanol to ensure it was clean and dry. The sample was weighed using an electronic balance and recorded as M0 (g). For pulp imprinting, take an appropriate amount of corrugated pulp (5g) and evenly coat it on the surface of the coated sample (coating area 50 mm × 50 mm); apply a pressure of 10 MPa to the coated surface using a standard pressure device and hold for 5 min (simulating the contact process between the corrugated roller teeth and the paperboard). After the pressure was released, the sample and pulp were placed in a constant temperature and humidity chamber at 25°C and 50% RH for 30 minutes to simulate the wet contact process in the production environment. Drying and curing: The sample was placed in an 80℃ oven for 2 hours to simulate the paperboard forming and drying process, so that the water in the pulp evaporated and the adhesive solidified, forming the most difficult-to-remove dry and solidified adhesive state. Rinse with water to remove non-adhesive parts. Rinse the sample surface with room temperature tap water (water pressure 0.2 MPa) for 30 seconds to remove loose adhering substances. Immediately use an ultrasonic cleaner to sonicate in pure water at 25℃ for 2 minutes (power 100 W) to thoroughly remove mechanical deposits; Wipe dry with a lint-free cloth and weigh using an electronic balance, recording the weight as M1 (g).

[0059] Residual pulp mass = M1 − M0 (g / m 2 ) Residual mass less than 0.1 g / m 2 "No obvious adhesion", 0.1~0.5g / m 2 "Slight adhesion", 0.5–1.0 g / m 2 The adhesion is described as "light to moderate," exceeding 1.0 g / m². 2 The label indicates "significant adhesion / severe adhesion".

[0060] The results of Examples 1 to 5 show that when the ratio of TTIP to ethanol is 1:3 to 1:5, the porosity of the coating is stable below 1.1%, and the salt spray resistance time exceeds 480 h, which is the optimal process window. When the ratio is 1:8, TiO2 generation is insufficient, and the performance is significantly reduced. When the ratio is 1:2, although the porosity is the lowest, the deep pore filling effect is not ideal.

[0061] Taking Example 1 as an example, the initial cobalt-based tungsten carbide coating had a porosity of 4.0% and a water contact angle of 70°, indicating that there were many interconnected pores inside the coating and the surface was only slightly hydrophobic. After the tetrabutyl titanate / ethanol impregnation and drying treatment at 120°C in step S1, the tetrabutyl titanate underwent in-situ hydrolysis and condensation to form TiO2 within the coating pores, significantly reducing the porosity to about 1.5%, greatly improving corrosion resistance and overall density. However, the surface contact angle only slightly increased to about 75°, indicating that the improvement was mainly in the internal pore structure, with limited impact on surface wettability. Subsequently, alkaline electrolytic polishing was performed in step S2, further reducing the porosity slightly to about 1.3%, improving surface roughness and local uneven deposition. At the same time, a large number of hydroxyl active sites were formed on the surface of TiO2 and tungsten carbide coating, and the water contact angle slightly decreased to 72°, creating conditions for the subsequent chemical bonding of silane coupling agents. In step S3, KH570 undergoes hydrolysis and condensation on the TiO2 surface and within the pores of the coating, forming a silane interface layer with organic functional end groups. The porosity is maintained at approximately 1.3%, while the water contact angle increases to 80°. In step S4, fluorinated acrylic resin is applied to the KH570-treated coating surface with a dry film thickness of 0.10 mm and cured at 45°C / 25 min and 65°C / 45 min to obtain an interface structure of TiO2 pore-filling phase, KH570 molecular bridge, and fluorinated acrylic resin top layer. At this point, the overall porosity of the coating is further reduced to approximately 1.2%, and the water contact angle is significantly increased to approximately 110°. While maintaining low porosity and high adhesion, the surface hydrophobicity and resistance to pulp adhesion are significantly improved, achieving a comprehensive improvement in addressing corrosion failure, fatigue spalling, and pulp adhesion problems caused by coating porosity.

[0062] Comparing the performance indicators of the coatings obtained in Example 1 and Example 6, the coating obtained in Example 1 had a salt spray resistance time exceeding 500 h, while the coating obtained in Example 6 had a salt spray resistance time of only 360 h, representing an extension of approximately 38%; the residual pulp mass decreased from approximately 0.5 g / m³ in Example 6. 2 The concentration decreased to approximately 0.2 g / m³ in Example 1. 2 This represents a 60% reduction. This difference stems from the low surface energy (approximately 20 mN / m) of the fluorinated acrylic resin and the chemical inertness of the fluorine segments, which more effectively prevents salt spray droplet wetting and corrosive components in the pulp, such as chloride ions and organic acids, from penetrating into micro-defects in the coating, thus significantly extending the service life of the coating in wet corrosive environments. Example 1: Wear volume was 0.032 mm. 3 Compared to 0.045mm in Example 6 3 The corrosion resistance is reduced by approximately 40%, with the low coefficient of friction (μ≈0.1) of fluorinated acrylic acid reducing the area of ​​fresh coating exposed during wear, thus indirectly enhancing corrosion resistance.

[0063] The difference between Comparative Example 2 and Example 1 is that the grafting step of KH570 is skipped. After filling the pores with TiO2 in step S1, the porosity of Comparative Example 2 decreased to 1.5%. However, due to the lack of KH570 molecular bridges, the acrylic resin in step S4 only physically adhered to the coating surface and could not effectively penetrate into the residual micropores to form a strong chemical bond. This resulted in a salt spray resistance time of only 300 h and pulp residue of 0.68 g / m³. 2 The performance was significantly lower than that of Example 1. KH570 is chemically bonded to the coating through Si-O-Ti / Si-O-WC covalent bonds, while the acryloyl end groups copolymerize with the resin, allowing the resin to deeply fill the micropores and form an interfacial cross-linking network, significantly reducing the porosity to 1.2% and improving the salt spray resistance to 500 h.

[0064] The TiO2 pore-filling, KH570 molecular bridge, and fluorinated acrylic resin top layer used in this invention form a mutually reinforcing synergistic relationship between pore structure control and surface interface regulation. On the one hand, the in-situ TiO2 pore filling significantly reduces the volumetric porosity of the coating, enabling the organic top layer to form a continuous film on a relatively dense and flat substrate, thereby weakening corrosion channels and mechanical interlocking sites from the source. On the other hand, the low surface energy and hydrophobic and oleophobic properties provided by the fluorinated acrylic resin inhibit the penetration of the pulp aqueous phase and organic components into the residual micropores, greatly reducing the formation of liquid bridges and dry-solid bridging, thus amplifying the contribution of pore filling to corrosion resistance and anti-adhesion under actual service conditions.

Claims

1. A method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roller, characterized in that: Includes the following steps: S1. The corrugated roller coated with tungsten carbide is immersed in a tetrabutyl titanate / ethanol solution, so that the tetrabutyl titanate penetrates into the coating pores and undergoes hydrolysis and condensation during the drying process, transforming in situ into titanium dioxide precursor and / or nano titanium dioxide in the coating pores to fill most of the pores in the coating. S2. Connect the corrugated roller that has passed through S1 to the positive terminal of the power supply as the anode of electrolytic processing, and the platinum carbon electrode as the cathode. Place the corrugated roller in an alkaline electrolyte for electrolytic polishing to uniformly shape the surface morphology of the tungsten carbide coating and generate hydroxyl reaction sites on the surface. S3. Place the corrugated roller that has passed through S2 into a KH570 ethanol solution. KH570 condenses on the coating surface, and one end of the silane coupling agent forms a hydrogen bond or a covalent bond with titanium dioxide. S4. Apply an acrylic resin coating to the surface of the corrugated roll that has passed through S3. The acrylic resin forms a strong chemical bond with the titanium dioxide and tungsten carbide coating in the pores through KH570 molecular bridges. The coating is then heated and cured, and naturally cooled and air-dried to obtain an interface structure of TiO2 pore-filling phase - KH570 molecular bridge - acrylic resin top layer for filling the pores of the tungsten carbide coating of the target corrugated roll.

2. The method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roller according to claim 1, characterized in that: In step S1, the volume ratio of tetrabutyl titanate to ethanol is 1:(3-5), the immersion temperature is 70℃, the immersion time is 2h, and then it is dried at 120℃ for 3h.

3. The method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roller according to claim 1, characterized in that: The alkaline electrolyte in step S2 comprises the following substances by mass fraction: 0.5% sodium nitrate; 0.4% sodium chloride; 0.5%–3% complexing agent; 1%–5% disodium hydrogen phosphate; 5%–15% glycerol and ethylene glycol combined; 0.1%–1% sodium gluconate; balance water; The pH was adjusted to 12 to 13 using sodium hydroxide, and the electrolysis temperature was controlled at 30 to 50°C.

4. The method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roll according to claim 1, characterized in that: In step S3, the KH570 ethanol solution contains 3%–5% KH570 by mass. The treatment temperature is room temperature, the treatment time is 30 min, followed by drying at 80 °C for 1 h.

5. The method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roll according to claim 1, characterized in that: The acrylic resin mentioned in step S4 is an aqueous emulsion with a solid content of 30%–50% and a viscosity of 2000–5000 mPa·s, containing an anchoring agent and a silane coupling agent; wherein the amount of anchoring agent added is 3%–10% of the solid mass of the acrylic resin. The amount of KH570 added is 1% to 5% of the solid mass of the acrylic resin; The glass transition temperature of the acrylic resin is not lower than 80°C.

6. The method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roll according to claim 1, characterized in that: In step S4, the acrylic resin coating is applied by scraping. The acrylic resin coating curing process includes the following steps: S41. Let stand at room temperature for 10-15 minutes until the surface is dry and leveled. S42, cure at 40-50℃ for 20-30 minutes; S43. Heat to 60-70℃ and hold for 45 minutes; S44. Allow to cool naturally at room temperature and air dry for 24 hours.

7. The method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roll according to claim 1, characterized in that: The tungsten carbide coating is a cobalt-based tungsten carbide coating; The cobalt-based tungsten carbide coating was prepared using supersonic flame spraying technology with an oxygen pressure of 0.56 MPa and a flow rate of 160 L / min, a propane pressure of 0.48 MPa and a flow rate of 17 L / min, a spraying distance of 275 mm, and a coating thickness of 250 μm.

8. The method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roll according to claim 7, characterized in that: The cobalt-based tungsten carbide coating powder comprises the following substances in parts by mass: Co powder, 1-6 parts; 0.5–2 parts of Cr3C2 powder; Vitamin C powder 0.5–2 parts; 90.0–94.5 parts of tungsten carbide powder.

9. The method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roll according to claim 7, characterized in that: The preparation method of cobalt-based tungsten carbide includes the following steps: S11. After uniformly mixing Co powder, Cr3C2 powder and VC, place them with tungsten carbide powder in a ball mill for spherical mixing. S12. Place the powder mixed in step S11 into a graphite negative mold and pre-press it using a hydraulic press. The pre-pressing pressure is 5-20 MPa and the holding time is 5 min. S13. Place the assembled graphite mold in the spark plasma sintering system, set the axial pressure to 0-50 MPa, evacuate to below 5 Pa, and sinter by powering on; set the heating rate to 5℃-30℃ / min, the sintering temperature to 1250℃-1450℃, and the holding time to 5-15 min. S14. The sample is removed using a hydraulic press, and the graphite on the sample surface is removed by grinding to obtain a cobalt-based tungsten carbide composite cemented carbide material.

10. The method for in-situ filling the pores of the tungsten carbide coating on the surface of a corrugated roll according to claim 1, characterized in that: The process parameters for immersing the corrugated roller in the tetrabutyl titanate / ethanol solution in step S1 are as follows: Immersion temperature: 65℃ to 75℃; Soaking time: 2 hours; Dry at 120℃ for 3 hours.

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