Roller EDT texturing electroplating process

Abstract

The invention provides a roller EDT texturing electroplating technology which comprises the following steps that heat treatment, pretreatment, EDT electric spark texturing and electrochemical surface treatment are conducted on a roller, so that the surface of the roller is plated with a chromium layer, the electrochemical surface treatment technology comprises reverse etching, electroplating and polishing which are sequentially conducted, the current density of reverse etching is 22-30 A / dm < 2 >, and the current density of electroplating is 20-30 A / dm < 2 >. The reverse etching time is 30 to 120 seconds; the current density of electroplating is 25-35 A / dm < 2 >, and the electroplating time is 10-15 minutes; polishing until the roughened working surface is a non-uniform rough surface; the electroplating solution comprises 200-300 g / L of chromic anhydride, 2-3 g / L of sulfuric acid and 10-50 g / L of a composite additive, and the composite additive comprises a film-forming agent, a stabilizer and a conductive agent; by means of the EDT texturing electroplating technology for the roller, the roller can have the Vickers hardness of 900 or above after chromium plating, and the service life of the roller is greatly prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of roll plating, and particularly relates to a roll EDT texturing electroplating process. BACKGROUND

[0002] In the process of rolling metal products, the roll as the core equipment, the surface state directly determines the quality and production efficiency of the products. In order to improve the hardness and wear resistance, so as to improve the service life of the roll, the roll surface is usually provided with a plating layer through an electroplating process. The material of the plating layer usually includes titanium, chromium, nickel and the like, or carbide alloy, which helps to realize stable engagement with the rolled metal product in the rolling process, reduce the friction coefficient, and prevent sticking. With the increasing demand for high-end plate materials such as automobile plate and household appliance panel, higher comprehensive requirements are put forward for the roll surface. It is required to maintain accurate and controllable surface roughness to form ideal deformation texture, and the plating layer is required to have sufficient hardness to resist rolling impact and abrasive wear.

[0003] To meet the above requirements, the industry has developed various plating hardness strengthening technologies. The traditional scheme mainly includes hot spraying to prepare carbide ceramic coating, electroplating hard chromium layer and laser cladding alloying layer. These strengthening technologies can improve the hardness of the roll surface to a certain extent, but the Vickers hardness upper limit is generally 700-800HV under the measurement of ultrasonic hardness tester. Due to temperature control, pores, oxide inclusions and incompletely melted particles cannot be avoided in the hot spraying and laser cladding process, which weakens the actual hardness performance of the effective bearing area.

[0004] The traditional electroplated hard chromium layer relies on the reduction reaction of chromium ions on the surface of the substrate to deposit layer by layer. A case of a steel plant shows that the first failure of the chromium-plated roll during service is not wear out of tolerance, but peeling failure caused by interface peeling. Scanning electron microscopy finds that there are obvious tearing edges on the peeling surface, which confirms that the shear stress is concentrated at the interface rather than the bulk material. Due to the difference in thermal expansion coefficient between the plating layer and the substrate, periodic tangential stress will be generated under alternating rolling load, which accelerates the fatigue damage of the interface.

[0005] Chinese patent (CN109807554B) provides a manufacturing process of a cold roll. After quenching treatment of the cold roll, an EDT electric spark texturing machine tool is used for texturing treatment of the working surface. The working surface is subjected to electrochemical passivation, so that the micro peak part prone to breakage and wear on the textured working surface is passivated due to the electrochemical deburring effect, and the service life of the EDT textured cold roll is greatly prolonged. However, for the roll prepared by the EDT electric spark texturing process, passivation also reduces the bonding effect of the textured working surface and the plating layer. SUMMARY

[0006] The present application aims at overcoming the deficiencies of the prior art, and providing a rolling mill roll EDT texturing electroplating process, which greatly improves the composite strength of the existing rolling mill roll surface plating layer and prolongs the service life of the rolling mill roll.

[0007] To achieve the above object, the technical scheme provided by the present application is as follows. A rolling mill roll EDT texturing electroplating process, comprising the following steps: S1, heat treating the rolling mill roll, wherein the heat treatment process comprises quenching and tempering treatment; S2, pretreating the rolling mill roll after the heat treatment, wherein the pretreatment process comprises fine turning, rough grinding, fine grinding and super fine grinding; S3, performing EDT electric spark texturing on the surface of the rolling mill roll after the pretreatment, wherein the EDT electric spark texturing process uses high-low alternating voltage to form recesses of different sizes on the surface of the rolling mill roll, and the recesses are unevenly distributed on the surface of the rolling mill roll; S4, placing the rolling mill roll after the EDT electric spark texturing treatment in an electrochemical treatment tank to perform electrochemical surface treatment, so that a chromium plating layer is provided on the surface of the rolling mill roll by electroplating, wherein the electrochemical surface treatment comprises reverse etching, electroplating and polishing performed in sequence, the electrochemical surface treatment is performed repeatedly for multiple times, and the thickness of the chromium plating layer is 10-30 μm.

[0008] As a preferred technical scheme, in the S1, the quenching temperature is 950-980 ℃, progressive induction quenching is used, the tempering temperature is 100-150 ℃, the holding time is 80-120 hours, and after the heat treatment, the surface hardness of the rolling mill roll reaches 66-67 HRC, without cracks and deformation.

[0009] As a preferred technical scheme, in the S2, 10-15% hydrochloric acid solution is used for pickling for 5-10 minutes, and after the treatment, the surface should be free of oxide skin and oil stains, and the uniformity of the surface roughness Ra is ≤0.2 μm.

[0010] As a preferred technical scheme, in the S3, the roughness Ra is controlled to be 0.8-2.0 μm, and the peak density PC is ≥100 points / cm 2 .

[0011] As a preferred technical scheme, in the S4, the current density of the reverse etching of the electrochemical surface treatment is 22-30 A / dm 2 , the reverse etching time is 30-120 seconds, the current density of the electroplating is 25-35 A / dm 2 , and the electroplating time is 10-15 minutes.

[0012] As a preferred technical scheme, in the electrochemical surface treatment, the polishing adopts at least one of mechanical polishing, chemical polishing, ultrasonic polishing, fluid polishing and magnetic abrasive finishing, and the roughness uniformity Ra of the roughened work surface is ≤0.1 μm.

[0013] As a preferred technical scheme, in the EDT electrospark roughening, the roll rotating speed is 20-60 rpm, the transverse moving speed is 1000-4000 mm / min, the electrode current is 30-62 A, the on-line time / off-line time is 5-999 μs, the electrospark frequency is 50-400 kHz, and the roughening medium is dielectric oil with conductive particle additives added.

[0014] As a preferred technical scheme, in the EDT electrospark roughening, the dielectric oil is used as the roughening medium, and the dielectric oil is a mineral oil-based or synthetic ester-based medium.

[0015] As a preferred technical scheme, the components of the electroplating solution include chromic anhydride 200-300 g / L, sulfuric acid 2-5 g / L, and composite additives 10-50 g / L, wherein the composite additives include at least one of film-forming agents, stabilizers and conductive agents.

[0016] As a preferred technical scheme, the concentration ratio of the chromic anhydride to the sulfate ion is 50:1, and the concentration of the sulfate ion is in the range of 1.8-2.5 g / L, part of the sulfate ions form mixed ligand complexes with trivalent chromium at the cathode, participate in deposition regulation and co-deposit with the plating layer.

[0017] As a preferred technical scheme, the working temperature of the electrochemical treatment tank is 50-60℃, the current density is 30-60 A / dm 2 The cathode electrode of the electrochemical treatment tank is the workpiece to be treated, the anode electrode of the electrochemical treatment tank is a Pb-Sn alloy, and the area ratio of the cathode electrode to the anode electrode is 1:2-1:3.

[0018] As a preferred technical scheme, the roll prepared by the roll EDT roughening electroplating process according to any one of the at least one technical feature is probed by an ultrasonic hardness tester, and the surface hardness is 900-950 HV.

[0019] The advantages and beneficial effects of the present application are that the roll EDT texturing electroplating process can produce an electroplated roll with a surface hardness of 900-950 HV, the roll produced by the present application has a steel passing capacity that is more than 10 times that of a roll without chromium plating, and more than 2 times that of a conventional chromium plated roll. The EDT texturing forms unevenly distributed micro-pits on the roll surface, increasing the bonding area of the plating layer and the substrate; through the reverse etching-electroplating-polishing process, deep deposition and surface optimization of the chromium plating layer are achieved, forming a high-density, high-strength combined columnar crystal structure; the introduction of the composite additive further regulates the cathode film thickness and electrical conductivity, inhibits the initiation of interface fatigue cracks, thereby improving the plating layer hardness, bonding force and wear resistance. DETAILED DESCRIPTION

[0020] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below. It can be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0021] The terms "comprising" and "having" and any variations thereof in the present application are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units that are not listed, or can optionally include other steps or units inherent to these processes, methods, products or devices.

[0022] In this document, referring to "embodiments" means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it mutually exclusive or alternative to other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0023] In the embodiments of the present application, a roll EDT texturing electroplating process is provided, which can produce a chromium plated roll with higher hardness and double the service life of the prior art.

[0024] Roller is the core working component and tool on the rolling mill, usually including roller body, roller neck and shaft head, wherein, the roller body is the part actually participating in rolling metal, the surface is smooth or with rolling groove; the roller neck is installed in the bearing, and the rolling force is transmitted to the rack; and the shaft head connects the transmission system, and the motor torque is transmitted to drive the roller to rotate. The function of the roller is to make the metal produce continuous plastic deformation through the extrusion action between the roller body and the metal blank, and finally form the required cross-sectional shape, and the surface precision of the roller directly affects the size tolerance, surface finish and mechanical properties of the rolled material.

[0025] The EDT roller texturing electroplating process of the application improves the hardness, adhesion and wear resistance of the chromium plating layer on the roller surface through optimization of heat treatment, pretreatment, EDT texturing and electrochemical surface treatment, forms unevenly distributed micro-pits through EDT texturing, increases the bonding area of the plating layer and the substrate, and realizes deep deposition and surface optimization of the chromium plating layer through reverse etching-electroplating-polishing, forming a high-density, high-strength combined columnar crystal structure. The introduction of composite additives further regulates the cathode film thickness and electrical conductivity, inhibits the initiation of interface fatigue cracks, thereby prolonging the service life of the roller.

[0026] The process first carries out accurate heat treatment on the roller, including quenching and tempering, so that the substrate has a high hardness of 58-62HRC and a crack-free microstructure, providing a strong and tough support foundation for the subsequent plating layer. In the pretreatment stage, mechanical polishing, oil removal and acid pickling activation are carried out to ensure that the surface is clean and has a suitable roughness, and to prepare the surface for EDT texturing.

[0027] EDT electric spark texturing is one of the key steps of the process. By using high-low alternating voltage, micro-pits of different sizes and unevenly distributed on the roller surface are formed, which not only increases the mechanical bonding area of the plating layer and the substrate, but also the controlled roughness and high peak density together constitute an ideal plating layer anchoring structure. During the texturing process, a specific formula of dielectric oil is used and conductive particles are added to enhance the discharge stability and texturing effect.

[0028] In the electroplating solution formula, the concentration ratio of chromic anhydride to sulfate ions is controlled at 50:1, which ensures the formation and stability of the cathode film. Sulfate not only acts as a catalyst to promote chromium deposition, but also forms a mixed ligand complex with trivalent chromium, participates in deposition regulation and co-deposits with the plating layer, further refining the grain structure. The introduction of composite additives (including film forming agent, stabilizer and conductive agent) regulates the cathode film properties, maintains the stability of the plating solution, and compensates for the electrical conductivity, thereby obtaining a more uniform and dense plating layer.

[0029] In some embodiments, the surface of the roll prepared by the process can have a surface hardness of 900-950 HV (Vickers hardness), such as 900 HV, 912 HV, 921 HV, 926 HV, 934 HV or 950 HV, as measured by ultrasonic hardness testing. The higher hardness reflects the good bonding effect between the plated layer on the roll surface and the roughened working surface of the roll, thereby improving the adhesion of the plated layer on the roll surface and reducing or eliminating peeling of the plated layer from the roll due to insufficient bonding between the plated layer and the roll during service of the chrome-plated roll.

[0030] In some embodiments, the roll after the pre-treatment is subjected to EDT electro-discharge texturing treatment. The core of the EDT electro-discharge texturing treatment is to use the principle of electric arc corrosion. In a conductive medium oil, an electric bridge between the electrode and the roll is established by a pulse generator to form a transient discharge channel. High-voltage pulses cause electric sparks between the electrode and the roll. The local high temperature causes the roll surface to melt slightly. The gasified substances produced by the discharge form bubbles. When the bubbles burst, the molten metal is thrown away from the surface to form small pits. By adjusting the current size, pulse frequency and electrode spacing, the density, size and distribution of the pits can be controlled to achieve the target surface roughness.

[0031] In some embodiments, the chrome layer is formed by reverse etching, electroplating and polishing in a cycle. The chrome atoms on the chrome layer can be cyclically deposited and optimized on the surface to form a structure with high density and high strength bonding. Reverse etching refers to a processing technology of reverse etching on the roll surface. The purpose is to selectively remove the material on the surface of the rolled workpiece so that the roll surface can be removed by etching. The deposited chrome layer may have uneven thickness. For the local thicker area of the plated layer, the essence is that the local thicker area has better electrical conductivity than the average thickness of the plated layer on the roll as a whole. Reverse etching uses this point to etch and thin the local area with relatively better electrical conductivity before improving or adjusting the electroplating process or adjusting the parameters for local improvement.

[0032] In some embodiments, the current density in the reverse etching stage is controlled at 22-30 A / dm 2 , and the time is 30-120 seconds. High-current pulses are used to remove oxides or impurities on the roughened working surface of the roll, such as carbides remaining after EDT treatment, and precipitates on the roll surface, activate the micro recesses on the surface, and improve the adsorption and bonding capacity of the subsequent plated layer. In some embodiments, the reverse etching current density is controlled at 22 A / dm 2 , 25 A / dm 2 , 28 A / dm 2 , 30 A / dm 2; in some embodiments, the etching time is controlled at 30 seconds, 45 seconds, 80 seconds, 120 seconds.

[0033] In some embodiments, the plating stage current density is 25-35 A / dm 2 , time 10-15 minutes. In this stage, chromium ions are reduced and deposited from the plating solution, and chromium atoms grow layer by layer on the activated surface to form a dense chromium layer with a crystal structure. Through multiple cycles, chromium atoms can be cyclically deposited to accumulate, and the final total thickness can reach 50-100 μm, which ensures the overall uniformity and high hardness of the plating layer. In some embodiments, the etching current density is controlled at 25 A / dm 2 , 28 A / dm 2 , 30 A / dm 2 , 35 A / dm 2 ; in some embodiments, the etching time is controlled at 90 minutes, 100 minutes, 120 minutes, 150 minutes.

[0034] In some embodiments, the polishing stage adopts mechanical polishing, fluid polishing or ultrasonic polishing, etc. Polishing not only removes the micro-protrusions and defects on the surface of the chromium plating layer, but also makes chromium atoms circulate to rearrange the surface, reduce internal porosity, and thus eliminate stress concentration points and avoid the initiation of interface fatigue cracks.

[0035] According to the EDT texturing electroplating process shown in the present application, the plating solution in the etching and plating process contains the following components: chromic anhydride 200-300 g / L, sulfuric acid 2-3 g / L, and composite additive 10-50 g / L, wherein the composite additive includes at least one of film-forming agent, stabilizer, and conductive agent.

[0036] The aqueous solution of chromic anhydride (CrO3) is chromic acid, in which chromium ions are reduced by electrons on the cathode (the workpiece to be plated, i.e. the roller) to form a chromium plating layer on the surface of the workpiece. Chromic acid and its related ions play a role in conducting electricity in the plating solution, and a suitable concentration of chromic acid helps to maintain the conductivity of the plating solution, ensuring the normal progress of the electroplating process, improving the dispersion and coverage of the plating solution, and enabling the plating solution to better deposit a chromium plating layer on sharp corners, grooves and other parts of the workpiece, thereby improving the uniformity and integrity of the plating layer. A suitable concentration of chromic acid can make the chromium crystal structure in the plating layer more dense, thereby increasing the hardness of the chromium plating layer and effectively resisting mechanical damage such as wear and tear.

[0037] Sulfuric acid, especially sulfate ions (SO4 2- ), acts as a cathode film-forming agent in the plating solution. In the cathode reaction, sulfate ions preferentially adsorb to the high current density area on the surface of the roller, and react with chromic acid ions (HCrO4 -) forming an alkaline chromium sulfate colloid film ([Cr(OH) 3 · Cr 2 (SO 4 ) 3 ]). The film has selective penetration characteristics, inhibits the rapid deposition of chromium ions at sharp corners / protrusions, homogenizes the reduction rate of chromium ions by controlling the cathode film resistance, and promotes the directional growth of the plated layer crystal structure into dense columnar crystals. It should be noted that part of the sulfate is combined with trivalent chromium as a colloidal precipitate in the reaction, and it is necessary to regularly detect the concentration and supplement to maintain the concentration ratio.

[0038] Chromium(III) is a necessary medium for cathode reduction reaction, which maintains the deposition efficiency through self-catalytic cycle with chromium(VI), and its concentration control is used to maintain the redox balance of the plating solution, prevent colloidal flocculation, and prevent surface defects of the chromium plated layer.

[0039] The composite additive includes but is not limited to at least one of a film forming agent, a stabilizer, and a conductive agent; wherein the film forming agent includes but is not limited to sodium benzenesulfonate, sodium o-sulfonate benzoyl imide, sodium 1,5-naphthalene disulfonate, and sodium dodecyl sulfate, which competes with sulfate for adsorption and regulates the thickness of the cathode film; the stabilizer includes but is not limited to sodium formate, sodium citrate, oxalic acid, and sodium acetate, which complexes free chromium(III) to prevent excessive oxidation and reduce hardness fluctuations in the chromium plated layer caused by the consumption of the electroplating solution; and the conductive agent includes but is not limited to cerium sulfate, potassium fluorosilicate, magnesium sulfate, and potassium chloride, which compensates for the conductivity under low sulfuric acid concentration and improves the dispersion ability of the plating solution.

[0040] The composite additive introduced in the present application competes for adsorption of the film forming agent and sulfate ions in the solution on the roll surface. This competition is not mutual inhibition, but dynamic adjustment of the thickness and density of the cathode film. The film forming agent preferentially adsorbs on the edges of the micro-pits with high current density, inhibiting the plating of chromium ions in these areas, guiding the chromium layer to fill the micro-pit bottom produced by EDT more uniformly, enhancing the mechanical interlocking and metallurgical bonding, and reducing the interface stress concentration caused by the morphology mutation. The role of the stabilizer is to complex trivalent chromium to prevent precipitation, and part of it participates in co-deposition, refining the plated layer grain to the nanometer scale. This fine-grain strengthening effect makes it easier for the plated layer hardness to break through 900HV. At the same time, these embedded organic molecules in the grain boundary to some extent alleviate the inherent brittleness of the hard chromium layer, making the plated layer not prone to micro-cracks under high rolling impact, achieving synchronous improvement of hardness and toughness. The addition of the conductive agent not only compensates for the possible decrease in conductivity due to the control of sulfuric acid concentration, but also changes the double-layer structure with rare earth ions, reducing the deposition overpotential of metal ions. This makes the deposition process more smooth and uniform under the same current density, widening the process window for obtaining high-quality plated layers.

[0041] The uneven surface formed by EDT texturing naturally has uneven current distribution. The current density is high at the protrusions and sharp corners, where chromium ions will preferentially and rapidly deposit, forming a rough and loose "dendritic" structure. The bottom of the depressions, on the other hand, is under-deposited. This results in uneven plating thickness, high internal stress, and stress concentration points at the protrusions, which become the source of cracks. The molecules of the film-forming agent compete with sulfate ions, which act as catalysts, for adsorption on the surface of the roll (cathode). These adsorbed organic molecules form a very thin but dense barrier film that blocks the rapid deposition of chromium ions in these areas. The concentration of trivalent chromium ions in the plating solution must be maintained within an optimal range. If the concentration is too low, the deposition reaction will be difficult to start and maintain; if the concentration is too high, defects such as pitting and nodules will occur in the plating layer. The functional groups in the stabilizer molecules can undergo complexation reactions with trivalent chromium ions, forming stable and soluble complexes that keep the chromium content in a dynamic stable environment. Some stabilizer molecules or their decomposition products can embed in the growing plating layer. They adsorb on the boundaries of chromium grains, inhibiting the excessive growth of grains, thereby refining the grains. In order to obtain an ideal plating layer structure, the concentration of sulfuric acid is intentionally controlled in this process. However, this reduces the conductivity of the plating solution, leading to an increase in cell voltage and energy consumption. The conductive agent ionizes a large number of unrelated cations and anions in the solution, increasing the ionic strength and conductivity of the plating solution, making it easier for current to pass to every corner of the workpiece, ensuring that the entire surface can obtain a plating layer with uniform thickness. At the same time, the stabilizer and the conductive agent work together to reduce the overall concentration polarization phenomenon of the electroplating solution.

[0042] In some embodiments, the working temperature of the electrochemical treatment tank is 50-60℃, the current density is 30-60A / dm 2 The cathode electrode of the electrochemical treatment tank is connected to the workpiece to be treated, i.e. the roll, and the anode electrode of the electrochemical treatment tank uses lead-tin alloy.

[0043] The application will be described in detail below with specific examples.

[0044]

Example 1

[0045] S2. The heat-treated rolls are pretreated by polishing through fine turning, rough grinding, fine grinding, and ultra-fine grinding, followed by degreasing, water washing, and acid pickling activation. Acid pickling uses a 10% hydrochloric acid solution for 5 minutes. After treatment, the surface is free of oxide scale and oil, and the surface roughness uniformity Ra ≤ 0.2 μm.

[0046] S3. The pretreated roll surface is then subjected to EDT (Electronic Discharge Machining). The EDT process uses alternating high and low voltages to create depressions of varying sizes on the roll surface, resulting in a non-uniform distribution of depressions. The surface roughness Ra is controlled at 0.8 μm, and the peak density PC ≥ 100 points / cm². 2 In EDT texturing, the roll speed is 20 rpm, the traverse speed is 1000 mm / min, the electrode current is 30 A, the duty cycle / unduration cycle is 5 μs, the spark frequency is 50 kHz, and the texturing medium is dielectric oil with added conductive particles. The dielectric oil is a mineral oil-based medium.

[0047] S4. The rolls that have undergone EDT (Electro-Discharge Machining) texturing are placed in an electrochemical treatment tank for electrochemical surface treatment. A chromium plating layer is then applied to the roll surface via electroplating. The electrochemical surface treatment includes sequential reverse etching, electroplating, and polishing, repeated multiple times to obtain a chromium plating layer with a thickness of 10 μm. The reverse etching current density is 22 A / dm³. 2 The engraving time is 30 seconds; the electroplating current density is 25 A / dm². 2 The electroplating time is 10 minutes. Polishing is performed mechanically until the roughness uniformity Ra of the roughened working surface is ≤0.1μm. The electrochemical treatment tank operates at a temperature of 50℃ and a current density of 30A / dm³. 2 The cathode electrode of the electrochemical treatment tank is the workpiece to be treated, and the anode electrode is a Pb-Sn alloy. The area ratio of the cathode electrode to the anode electrode is 1:2. The electroplating solution consists of 200 g / L chromic anhydride, 2 g / L sulfuric acid, and 10 g / L composite additives, including sodium benzenesulfonate as a film-forming agent. The concentration ratio of chromic anhydride to sulfate ions is 50:1, and the sulfate concentration ranges from 1.8 g / L. Some sulfate ions form mixed ligand complexes with trivalent chromium at the cathode, participating in deposition regulation and co-depositing with the coating.

[0048] The rolls produced in this embodiment were tested with an ultrasonic hardness tester, and their surface hardness was found to be 900 HV.

[0049]

Example 2

[0050] S2. The heat-treated rolls are pretreated by polishing through fine turning, rough grinding, fine grinding, and ultra-fine grinding, followed by degreasing, water washing, and acid pickling activation. The acid pickling uses a 12% hydrochloric acid solution for 7 minutes. After treatment, the surface is free of oxide scale and oil, and the surface roughness uniformity Ra ≤ 0.2 μm.

[0051] S3. The pretreated roll surface is then subjected to EDT (Electronic Discharge Machining). The EDT process uses alternating high and low voltages to create depressions of varying sizes on the roll surface, resulting in a non-uniform distribution of depressions. The surface roughness Ra is controlled at 1.2 μm, and the peak density PC ≥ 100 points / cm². 2 In EDT texturing, the roll speed is 35 rpm, the traverse speed is 2000 mm / min, the electrode current is 45 A, the duty cycle / unduration cycle is 200 μs, the spark frequency is 150 kHz, and the texturing medium is dielectric oil with added conductive particles. The dielectric oil is a synthetic ester-based medium.

[0052] S4. The rolls that have undergone EDT (Electro-Discharge Machining) texturing are placed in an electrochemical treatment tank for electrochemical surface treatment. A chromium plating layer is then formed on the roll surface through electroplating. The electrochemical surface treatment includes sequential reverse etching, electroplating, and polishing, repeated multiple times to obtain a chromium plating layer with a thickness of 15 μm. The reverse etching current density is 25 A / dm³. 2 The engraving time is 60 seconds; the electroplating current density is 28 A / dm³. 2 The electroplating time is 12 minutes. Polishing is performed using ultrasonic polishing until the roughness uniformity Ra of the roughened working surface is ≤0.1μm. The electrochemical treatment tank operates at a temperature of 53℃ and a current density of 40A / dm³. 2 The cathode electrode of the electrochemical treatment tank is the workpiece to be treated, and the anode electrode is a Pb-Sn alloy. The area ratio of the cathode electrode to the anode electrode is 1:2.5. The electroplating solution consists of 230 g / L chromic anhydride, 3 g / L sulfuric acid, and 25 g / L composite additives. The composite additives include the stabilizer sodium formate and the conductive agent (such as rare earth metal salts). The concentration ratio of chromic anhydride to sulfate ions is 50:1, and the sulfate concentration ranges from 2.0 g / L. Some sulfate ions form mixed ligand complexes with trivalent chromium at the cathode, participating in deposition regulation and co-depositing with the coating.

[0053] The rolls produced in this embodiment were tested with an ultrasonic hardness tester, and their surface hardness was found to be 920 HV.

[0054]

Example 3

[0055] S2. The heat-treated rolls undergo pretreatment, which includes polishing via precision turning, rough grinding, fine grinding, and ultra-fine grinding. Then, the rolls are degreased, washed with water, and activated by acid pickling. Acid pickling uses a 14% hydrochloric acid solution for 8 minutes. After treatment, the surface is free of oxide scale and oil, and the surface roughness uniformity Ra ≤ 0.2 μm.

[0056] S3. The pretreated roll surface is then subjected to EDT (Electronic Discharge Machining). The EDT process uses alternating high and low voltages to create depressions of varying sizes on the roll surface, resulting in a non-uniform distribution of depressions. The surface roughness Ra is controlled at 1.6 μm, and the peak density PC ≥ 100 points / cm². 2 In EDT texturing, the roll speed is 50 rpm, the traverse speed is 3000 mm / min, the electrode current is 55 A, the on-line time / off-line time is 500 μs, the spark frequency is 300 kHz, and the texturing medium is dielectric oil with added conductive particles. The dielectric oil is a mineral oil-based medium.

[0057] S4. The rolls that have undergone EDT (Electro-Discharge Machining) texturing are placed in an electrochemical treatment tank for electrochemical surface treatment. A chromium plating layer is then applied to the roll surface via electroplating. The electrochemical surface treatment includes sequential reverse etching, electroplating, and polishing, repeated multiple times to achieve a chromium plating layer thickness of 25 μm. The reverse etching current density is 28 A / dm³. 2 The engraving time is 90 seconds; the electroplating current density is 32 A / dm³. 2 The electroplating time is 14 minutes. Polishing is performed using fluid polishing until the roughened surface roughness uniformity Ra ≤ 0.1 μm. The electrochemical treatment tank operates at a temperature of 57℃ and a current density of 50 A / dm³. 2The cathode electrode of the electrochemical treatment tank is the workpiece to be treated, and the anode electrode is a Pb-Sn alloy. The area ratio of the cathode electrode to the anode electrode is 1:2.8. The electroplating solution consists of 270 g / L chromic anhydride, 4 g / L sulfuric acid, and 40 g / L composite additives. The composite additives include sodium o-sulfonylbenzeneimide (a film-forming agent), sodium citrate (a stabilizer), and potassium fluorosilicate (a conductive agent). The concentration ratio of chromic anhydride to sulfate ions is 50:1, and the sulfate concentration ranges from 2.3 g / L. Some sulfate ions form mixed ligand complexes with trivalent chromium at the cathode, participating in deposition regulation and co-depositing with the plating layer.

[0058] The rolls produced in this embodiment were tested with an ultrasonic hardness tester, and their surface hardness was found to be 940 HV.

[0059]

Example 4

[0060] S2. The heat-treated rolls are pretreated by polishing through fine turning, rough grinding, fine grinding, and ultra-fine grinding, followed by degreasing, water washing, and acid pickling activation. Acid pickling is performed using a 15% hydrochloric acid solution for 10 minutes. After treatment, the surface is free of oxide scale and oil, and the surface roughness uniformity Ra ≤ 0.2 μm.

[0061] S3. The pretreated roll surface is then subjected to EDT (Electrical Discharge Testing) texturing. The EDT texturing process uses alternating high and low voltages to create depressions of varying sizes on the roll surface, resulting in a non-uniform distribution of depressions. The surface roughness Ra is controlled at 2.0 μm, and the peak density PC ≥ 100 points / cm². During EDT texturing, the roll speed is 60 rpm, the traverse speed is 4000 mm / min, the electrode current is 62 A, the duty cycle / unduration cycle is 999 μs, the spark frequency is 400 kHz, and the texturing medium is dielectric oil with added conductive particles. The dielectric oil is a synthetic ester-based medium.

[0062] S4. The rolls that have undergone EDT (Electro-Discharge Machining) texturing are placed in an electrochemical treatment tank for electrochemical surface treatment. A chromium plating layer is then formed on the roll surface through electroplating. The electrochemical surface treatment includes sequential reverse etching, electroplating, and polishing, repeated multiple times to obtain a chromium plating layer with a thickness of 30 μm. The reverse etching current density is 30 A / dm³. 2The engraving time is 120 seconds; the electroplating current density is 35 A / dm³. 2 The electroplating time is 15 minutes. Polishing is performed using magnetic abrasive polishing until the roughness uniformity Ra of the roughened working surface is ≤0.1μm. The electrochemical treatment tank operates at a temperature of 60℃ and a current density of 60A / dm³. 2 The cathode electrode of the electrochemical treatment tank is the workpiece to be treated, and the anode electrode is a Pb-Sn alloy. The area ratio of the cathode electrode to the anode electrode is 1:3. The electroplating solution consists of 300 g / L chromic anhydride, 5 g / L sulfuric acid, and 50 g / L composite additives. The composite additives include oxalic acid as a stabilizer and magnesium sulfate as a conductive agent. The concentration ratio of chromic anhydride to sulfate ions is 50:1, and the sulfate concentration ranges from 2.5 g / L. Some sulfate ions form mixed ligand complexes with trivalent chromium at the cathode, participating in deposition regulation and co-depositing with the coating.

[0063] The rolls produced in this embodiment, when tested with an ultrasonic hardness tester, have a surface hardness of 950 HV.

[0064] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A roll EDT texturing electroplating process, characterized in that, Includes the following steps: S1. The rolls are subjected to heat treatment, the heat treatment process including quenching and tempering; S2. The heat-treated rolls are pre-treated, and the pre-treatment process includes precision turning, rough grinding, fine grinding, and ultra-fine grinding. S3. The pre-treated roll surface is subjected to EDT (Electrical Discharge Testing) texturing. The EDT texturing process uses alternating high and low voltages to form depressions of different sizes on the roll surface. The depressions are unevenly distributed on the roll surface. S4. The rolls that have undergone EDT (Electro-Discharge Machining) are placed in an electrochemical treatment tank for electrochemical surface treatment, so that a chromium plating layer is formed on the surface of the rolls by electroplating. The electrochemical surface treatment includes reverse engraving, electroplating and polishing in sequence. The electrochemical surface treatment is repeated multiple times to obtain a chromium plating layer with a thickness of 10-30 μm.

2. The EDT texturing electroplating process according to claim 1, characterized in that, In S1, the quenching temperature is 950-980℃, using progressive induction quenching, the tempering temperature is 100-150℃, the holding time is 80-120 hours, and the surface hardness of the roll after heat treatment reaches 66-67HRC, with no cracks or deformation.

3. The EDT texturing electroplating process according to claim 1, characterized in that, S2 also includes pickling with a 10-15% hydrochloric acid solution for 5-10 minutes. After treatment, the surface should be free of oxide scale and oil stains, and the surface roughness uniformity Ra≤0.2μm.

4. The EDT texturing electroplating process according to claim 1, characterized in that, In S3, the roughness Ra is controlled between 0.8 and 2.0 μm, and the peak density PC is ≥ 100 points / cm². 2 .

5. The EDT texturing electroplating process according to claim 1, characterized in that, In step S4, the current density for electrochemical surface treatment reverse etching is 22-30 A / dm². 2 The engraving time is 30-120 seconds; the electroplating current density is 25-35 A / dm². 2 The electroplating time is 10-15 minutes; And / or, in the electrochemical surface treatment, polishing is performed using at least one of mechanical polishing, chemical polishing, ultrasonic polishing, fluid polishing, and magnetic abrasive polishing, until the roughness uniformity Ra of the roughened working surface is ≤0.1μm; And / or, in the EDT texturing process, the roll speed is 20-60 rpm, the traverse speed is 1000-4000 mm / min, the electrode current is 30-62 A, the on-line time / off-line time is 5-999 μs, the electric spark frequency is 50-400 kHz, and the texturing medium is dielectric oil containing conductive particle additives.

6. In the EDT texturing electroplating process according to claim 5, in the EDT electrical discharge texturing, a dielectric oil is used as the texturing medium, and the dielectric oil is a mineral oil-based or synthetic ester-based medium.

7. The EDT texturing electroplating process according to claim 6, characterized in that, The electroplating solution comprises 200-300 g / L of chromic anhydride, 2-5 g / L of sulfuric acid, and 10-50 g / L of composite additives, wherein the composite additives include at least one of film-forming agents, stabilizers, and conductive agents.

8. The EDT texturing electroplating process according to claim 7, characterized in that, The concentration ratio of chromic anhydride to sulfate ions is 50:1, and the concentration of sulfate ions ranges from 1.8 to 2.5 g / L. Some sulfate ions form mixed ligand complexes with trivalent chromium at the cathode, participate in deposition regulation, and are co-deposited with the coating.

9. In the EDT texturing electroplating process according to claim 5, the operating temperature of the electrochemical treatment tank is 50-60℃, and the current density is 30-60A / dm³. 2 The cathode electrode of the electrochemical treatment tank is the workpiece to be treated, and the anode electrode of the electrochemical treatment tank is a Pb-Sn alloy. The area ratio of the cathode electrode to the anode electrode is 1:2-1:

3.

10. The roll produced by the EDT texturing electroplating process according to any one of claims 1-9, characterized in that, When tested with an ultrasonic hardness tester, its surface hardness is 900-950 HV.