Electroplated nickel-cobalt / tungsten alloy double-layer composite coating on inner wall of gas cylinder as well as preparation method and application of electroplated nickel-cobalt / tungsten alloy double-layer composite coating

Abstract

The invention discloses an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder and a preparation method and application thereof.The preparation method comprises the steps that firstly, a nickel-cobalt coating is electroplated on the inner wall of the gas cylinder, then a tungsten alloy coating continues to be electroplated on the surface of the nickel-cobalt coating, conformal anodes are adopted during electroplating of the nickel-cobalt coating and the tungsten alloy coating, and the nickel-cobalt coating and the tungsten alloy coating are sequentially electroplated; when the nickel-cobalt plating layer and the tungsten alloy plating layer are electroplated, the area ratio of the cathode to the anode is controlled to be (1.5-2.0): 1; according to the electroplated nickel-cobalt / tungsten alloy double-layer composite coating provided by the invention, corrosion does not occur in 1500 hours in a neutral salt spray experiment; according to the invention, the tungsten alloy coating can completely ensure that the substrate is protected by the coating, can better play the roles of corrosion resistance and wear resistance of the tungsten alloy coating, can resist the corrosion of sodium chloride and sulfide, and meets the use requirements of high pressure resistance and erosion resistance of the gas cylinder in a marine environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of electroplating, and in particular relates to an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder, and a preparation method and application thereof. Background Art

[0002] With the vigorous development of the shipbuilding industry and China's marine industry, various gas cylinders used for gas storage have become a hot industry. Various ships and submarines, offshore operating platforms, ocean ports, etc. need to be equipped with gas cylinder products for breathing, medical treatment, engine oxygen supplementation, and metal cutting. The large-scale, high-pressure, and high-end performance requirements of gas cylinders are the high-end demands of the industrial chain. In 2022, the output of gas cylinders will be more than 2,000, and by 2025, the output of gas cylinders will reach more than 3,000. In particular, the use of gas cylinders in the military industry has increased significantly. Among them, more than 50% of the output requires surface treatment. With the high-end performance requirements of gas cylinders, the wear resistance and corrosion resistance of the chemical nickel surface treatment technology originally used cannot meet the requirements of high-end products. The working environment of high-pressure air cylinders is relatively harsh (working pressure: ≤60MPa, gas flow: >100Nm 3 / h), and the compressed air will contain a certain amount of condensed water (containing a certain amount of Cl - ), under the action of alternating dry and wet working media and stress, local corrosion will occur on the inner surface of the gas cylinder and aggravate the stress corrosion sensitivity of the high-strength cylinder body. If local corrosion occurs on the base of the gas cylinder, under the action of stress, the corrosion pit position will take precedence as the crack source, which will cause accelerated corrosion and cause its stress concentration factor to increase significantly, exceeding the fatigue limit of the material, causing fatigue failure of the gas cylinder and having an adverse impact on the safety and reliability of the gas cylinder. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the first object of the present invention is to provide a method for preparing an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder.

[0004] The second object of the present invention is to provide an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder prepared by the above preparation method.

[0005] The third object of the present invention is to provide an application of an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder prepared by the above-mentioned preparation method.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder. The method comprises the following steps: first, electroplating a nickel-cobalt coating on the inner wall of the gas cylinder; and then electroplating a tungsten alloy coating on the surface of the nickel-cobalt coating. When electroplating the nickel-cobalt coating and the tungsten alloy coating, a pictographic anode is used. The pictographic anode comprises a central conductive shaft, on which is provided an expandable anode sheet and a support device for driving the anode sheet to expand outward. Before the anode sheet expands, the radial dimension of the pictographic anode is smaller than the diameter of the gas cylinder mouth. When the pictographic anode enters the gas cylinder through the gas cylinder mouth, the outward expansion of the anode sheet controls the electroplating of the nickel-cobalt coating and the electroplating of the tungsten alloy coating, so that the area ratio of the cathode to the anode is 1.5-2.0:1.

[0008] The nickel-cobalt coating contains Ni and Co, wherein the mass fraction of Co in the nickel-cobalt coating is 8-12%, and the mass fraction of Ni is 88-91%; the tungsten alloy coating contains W, Ni, and P, wherein the mass fraction of W in the tungsten alloy coating is 12-30%, the mass fraction of Ni is 65-88%, and the mass fraction of P is 0.5-5%.

[0009] The present invention provides a method for preparing a double-layer electroplated nickel-cobalt / tungsten alloy composite coating on the inner wall of a gas cylinder. The method comprises electroplating a nickel-cobalt coating on the inner wall of the gas cylinder, and then electroplating a tungsten alloy coating on the surface of the nickel-cobalt coating. Utilizing the depth capability, throwing power, and high current effect of the nickel-cobalt plating solution, a nickel-cobalt alloy coating is electroplated on the inner wall of the gas cylinder to evenly fill the rough surface. A highly corrosion-resistant tungsten alloy coating is then applied to the outer surface to further ensure full coverage of the surface coating and reduce the risk of plating leaks. Simultaneously, a tungsten alloy coating is electroplated on the nickel-cobalt coating to enhance the protective effect of the coating on the substrate.

[0010] The electroplated nickel-cobalt / tungsten alloy double-layer composite coating prepared by the preparation method of the present invention has slightly larger grains of the nickel-cobalt coating and smaller grains of the tungsten alloy coating, so that the grains of the outer tungsten alloy coating and the inner nickel-cobalt coating will produce a double-layer dislocation structure, and the dislocation arrangement can effectively eliminate the porosity of the coating. The tungsten alloy coating is composed of a nickel-cobalt coating bonded to the substrate as a base layer and a tungsten alloy coating as an outer layer. The tungsten alloy coating has high hardness, good self-passivation, and strong wear and erosion resistance. The tungsten alloy coating has a more negative corrosion potential than the nickel-cobalt coating, and acts as a sacrificial anode layer during the corrosion process, so it is not easy to corrode. If the surface Damage will form a large anode on the surface and a small cathode structure on the bottom layer. During the electrochemical corrosion process, the tungsten alloy coating serving as the anode will be corroded first, while the nickel-cobalt coating serving as the cathode can be well protected. In this way, the double-layer composite coating as a whole forms an effective electrochemical protection for the gas cylinder, reducing the risk of longitudinal pitting corrosion. Therefore, the double-layer composite coating of the present invention has the performance characteristics of fatigue resistance, high toughness, high hardness, wear resistance, strong corrosion resistance and gas erosion resistance. The coating is used to isolate the contact between the marine atmospheric condensate corrosive medium and the substrate, which can greatly improve the safety of the gas cylinder and extend its service life.

[0011] The preparation method of the present invention uses tungsten alloy coating alone or tungsten alloy coating alone, in addition to being unable to form the synergistic effect described above, taking the tungsten alloy coating alone as an example, the current efficiency of the coating is not high, the coating coverage of the special-shaped gas cylinder is uneven, and the plating depth capacity is not strong. It is impossible to ensure 100% coverage when electroplating on the surface within 500mm of the two ports of the gas cylinder after high temperature treatment, especially the gas cylinder. It is easy to cause the risk of plating leakage and fail to protect the substrate. In addition, since the gas cylinder is a special-shaped part, the conventional anode is either unable to enter the gas cylinder or The inability to effectively control the appropriate area ratio of the cathode (inner wall of the gas cylinder) to the anode affects the uniformity of the coating at different locations in the gas cylinder. Therefore, the pictographic anode provided in the present invention has an expandable anode sheet. Before the anode sheet expands, the radial dimension of the pictographic anode is smaller than the diameter of the gas cylinder mouth. When the pictographic anode enters the gas cylinder from the gas cylinder mouth, the anode sheet expands outward and approaches the inner wall of the gas cylinder. When electroplating a nickel-cobalt coating layer and a tungsten alloy coating layer, the area ratio of the cathode to the anode is controlled to be 1.5-2.0:1, thereby ensuring uniform electroplating.

[0012] In a preferred embodiment, the pictographic anode includes a central conductive axis, and a plurality of anode sheet groups are axially arranged around the central conductive axis. In the anode sheet group located at the top of the pictographic anode, a fixed ring is provided at the top and fixed on the central conductive axis. The two ends of the remaining anode sheet groups and the bottom end of the anode sheet group located at the top of the pictographic anode are welded to the movable ring. An opening device is provided on the central conductive axis away from the fixed ring. When the pictographic anode enters the gas cylinder from the cylinder mouth, the opening device moves toward the fixed ring, so that the movable rings on the central axis move closer to each other, and drive the anode sheet to expand and bend outward, causing the anode sheet group to be "lantern-shaped".

[0013] Experiments have found that the anode sheet needs to be segmented to form several groups of "lantern-shaped" structures inside the gas cylinder in order to control the area of ​​the cathode and the anode to be 1.5-2.0:1. If the anode sheet is not segmented and only one group of anode sheets is used, it will expand to form a long lantern-shaped anode that runs through the entire gas cylinder. Not only will the distance between the anode and the cathode at both ends be too far, but the area ratio of the cathode to the anode cannot reach between 1.5-2.0:1, which ultimately leads to uneven coating.

[0014] In a further preferred embodiment, the number of the anode sheet groups is three. Experiments have shown that arranging the anode sheets into three groups forms three "lantern-shaped" structures in the gas cylinder, which results in the most uniform coating thickness and performance.

[0015] Further preferably, the width of the anode sheet is 15-25 mm. Experiments have found that when the width of the anode sheet is controlled within the above range, the coating performance is optimal.

[0016] In a preferred embodiment, the material of the pictographic anode is selected from titanium ruthenium coated metal oxide, titanium iridium coated metal oxide, and stainless steel.

[0017] The preferred solution is to pre-treat the inner wall of the gas cylinder in sequence, washing with hot water, washing with cold water, activating, washing with tap water, washing with deionized water, and then electroplating a layer of nickel-cobalt coating.

[0018] Further preferably, the pretreatment is to sequentially perform sandblasting, chemical degreasing and electrolytic degreasing on the inner wall of the gas cylinder.

[0019] Further preferably, the activation is to perform electrical activation and chemical activation on the inner wall of the pretreated gas cylinder in sequence, the process of the electrical activation is to place the pretreated inner wall of the gas cylinder in a nitrate solution for electrical activation for 10-20 minutes, the concentration of the nitrate solution is 380-420g / L, and the process of the chemical activation is to use a sulfuric acid solution with a mass fraction of 8-12% for activation for 5-10 minutes.

[0020] In a preferred embodiment, the electroplating solution A for the nickel-cobalt electroplating layer comprises nickel sulfate: 340-380 g / L, cobalt sulfate: 40-55 g / L, citric acid: 15-25 g / L, and boric acid: 25-35 g / L; when the nickel-cobalt electroplating layer is applied, the current density is 1-10 A / dm 2 , preferably 2-5A / dm 2 , further preferably 2-4A / dm 2 , the temperature is 30-60°C, preferably 45-55°C, the pH is 2.0-5.0, preferably 3.0-4.5, (the pH of the solution after plating is ≥3.0).

[0021] In a preferred embodiment, the electroplating solution B for the tungsten alloy coating comprises nickel sulfate: 14-22 g / L, sodium tungstate: 25-35 g / L, phosphorous acid: 20-30 g / L, citric acid: 30-180 g / L, and sodium citrate: 30-100 g / L. When the tungsten alloy coating is electroplated, the current density is 3-15 A / dm 2 , preferably 4-12A / dm 2 , more preferably 5-7A / dm 2 , the temperature is 50-80°C, preferably 55-75°C, and the pH is 5.0-8.0, preferably pH 6.5-7.5.

[0022] The nickel-cobalt coating has a large current effect, resulting in slightly larger coating grains; while the tungsten alloy has a small current effect, resulting in a dense coating and small grains. Therefore, the density of the outer tungsten alloy coating can well compensate for the defect of large grains in the nickel-cobalt coating. As a result, the outer tungsten alloy and the inner nickel-cobalt coating grains will produce a double-layer dislocation structure, and the dislocation arrangement can effectively eliminate the porosity of the coating.

[0023] In a preferred solution, when the nickel-cobalt coating and the tungsten alloy coating are electroplated, the gas cylinder is vertically fixed on the bracket.

[0024] In a preferred embodiment, an upper box body is provided at the upper end of the gas cylinder and a lower box body is provided at the lower end. When the nickel-cobalt coating and the tungsten alloy coating are electroplated, a portion of the electroplating solution A or the electroplating solution B enters from the inlet of the lower box body and flows out from the overflow port of the upper box body, forming a closed solution flow inside.

[0025] Through the above arrangement, during electroplating, the inner wall of the gas cylinder is subjected to circulating flow electroplating, which can further improve the uniformity of the thickness of the inner wall of the gas cylinder and the uniformity of the performance.

[0026] More preferably, the flow rate of the solution is ≥185 L / min.

[0027] In a preferred embodiment, air agitation is performed at the bottom of the gas cylinder during electroplating of the nickel-cobalt and tungsten alloy coatings. Experimental findings indicate that air agitation is crucial during electroplating. Failure to do so can negatively impact the density and uniformity of the coatings and cause plating impurities to fall off, forming dust nodules.

[0028] Further preferably, the intensity of the air stirring is 0.5-0.8m 3 / (min·m 2 The best performance is achieved by controlling the intensity of air stirring within this range. If it is too strong, a large number of stirring bubbles will be generated in the solution, causing local plating leakage. If it is too weak, it will not play a stirring role, and the solution will easily stratify and cause impurities to precipitate and form nodules on the surface of the coating.

[0029] In actual operation, after the tungsten alloy coating is electroplated, it is washed with deionized water, blown dry, and dehydrogenated.

[0030] The present invention also provides an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder prepared by the above preparation method, wherein the electroplated nickel-cobalt / tungsten alloy double-layer composite coating consists of a nickel-cobalt coating and a tungsten alloy coating from the inside to the outside.

[0031] Further preferably, the thickness of the nickel-cobalt coating is 20-45 μm, preferably 40-45 μm, and the thickness of the tungsten alloy coating is 10-20 μm, preferably 14-20 μm.

[0032] In the present invention, the performance is optimal when the thickness of each coating layer is controlled within the above range. If the coating thickness is lower than the controlled value, the corrosion resistance of the coating will be affected. If the coating is too thick, it will not only increase the cost, but also affect the bonding strength between the tungsten alloy surface coating and the substrate.

[0033] The present invention also provides an application of the electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder prepared by the above preparation method, and the gas cylinder containing the electroplated nickel-cobalt / tungsten alloy double-layer composite coating is applied in a marine environment.

[0034] Principles and advantages

[0035] The electroplated nickel-cobalt / tungsten alloy double-layer composite coating provided by the present invention has slightly larger grains of the nickel-cobalt coating and smaller grains of the tungsten alloy coating, so that the grains of the outer tungsten alloy coating and the inner nickel-cobalt coating will produce a double-layer dislocation structure, and the dislocation arrangement can effectively eliminate the porosity of the coating. The coating is composed of a nickel-cobalt coating bonded to the substrate as a base layer and an outer tungsten alloy coating. The tungsten alloy coating has high hardness, good self-passivation, and strong wear and erosion resistance. The tungsten alloy coating has a more negative corrosion potential than the nickel-cobalt coating, and acts as a sacrificial anode layer during the corrosion process, so it is not easy to corrode. If surface damage occurs, A large anode on the surface and a small cathode on the bottom layer will be formed. During the electrochemical corrosion process, the tungsten alloy coating as the anode will be corroded first, while the nickel-cobalt coating as the cathode can be well protected. In this way, the double-layer composite coating as a whole forms an effective electrochemical protection for the gas cylinder, reducing the risk of longitudinal pitting corrosion. Therefore, the double-layer composite coating of the present invention has the performance characteristics of fatigue resistance, high toughness, high hardness, wear resistance, strong corrosion resistance, and gas erosion resistance. The coating is used to isolate the contact between the marine atmospheric condensate corrosive medium and the substrate, which can greatly improve the safety of the gas cylinder and extend its service life. The electroplated nickel-cobalt / tungsten alloy double-layer composite coating provided by the present invention can achieve 1500 hours of no corrosion in the neutral salt spray test in the best case; the electroplated nickel-cobalt / tungsten alloy double-layer composite coating can 100% ensure that the substrate is protected by the coating, can better play the role of corrosion resistance and wear resistance of the tungsten alloy coating, and can resist sodium chloride and sulfide corrosion, meeting the use requirements of gas cylinders in marine environments with high pressure and erosion resistance.

[0036] The preparation method provided by the present invention is that since the gas cylinder is a special-shaped part, conventional anodes either cannot enter the gas cylinder or cannot effectively control the appropriate area ratio of the cathode and the anode, thereby affecting the uniformity of the coating at different parts of the gas cylinder. Therefore, the pictographic anode provided by the present invention has an expandable anode sheet. Before the anode sheet is expanded, the radial dimension of the pictographic anode is smaller than the diameter of the gas cylinder mouth. When the pictographic anode enters the gas cylinder from the gas cylinder mouth, the anode sheet expands outward to approach the inner wall of the gas cylinder. When controlling the electroplating of nickel-cobalt coating and the electroplating of tungsten alloy coating, the area ratio of the cathode and the anode is 1.5-2.0:1; thereby ensuring uniform electroplating. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the device for electroplating the inner wall of the gas cylinder in the present invention, in which 1-exhaust pipe, 2-air inlet pipe, 3-liquid outlet pipe, 4-upper box, 5-anode plate, 6-center conductive shaft, 7-cathode conductive clamp, 8-gas cylinder, 9-lower box, 10-anode conductive clamp, 11-stand, 12-liquid inlet pipe, 13-inflating pipe.

[0038] Figure 2 This is a schematic diagram of the process of the pictographic anode entering the gas cylinder to the expanded state in the present invention.

[0039] Figure 3 Microstructure diagram of the electroplated nickel-cobalt / tungsten alloy double-layer composite coating prepared in Example 1.

[0040] Figure 4 Microstructure diagram of the electroplated nickel-cobalt / tungsten alloy double-layer composite coating prepared in Example 1. DETAILED DESCRIPTION

[0041] In the following examples, the gas cylinder is placed on the bracket during electroplating. Figure 1 As shown, an upper box body is provided at the upper end of the gas cylinder, and a lower box body is provided at the lower end. When the nickel-cobalt coating and the tungsten alloy coating are electroplated, the electroplating solution A and the electroplating solution B enter from the inlet of the lower box body and flow out from the overflow port of the upper box body, forming a closed solution flow inside.

[0042] In addition, during electroplating, a pictographic anode is used. The pictographic anode includes a central conductive axis, and several anode sheet groups are arranged axially around the central conductive axis, preferably three groups. The width of the anode sheet is preferably 15-25 mm. In the anode sheet group located at the top of the pictographic anode, a fixed ring is provided at the top to be fixed on the central conductive axis. The two ends of the remaining anode sheet groups and the bottom end of the anode sheet group located at the top of the pictographic anode are welded to a movable ring. A support device is provided on the central conductive axis away from the fixed ring. When the pictographic anode enters the gas cylinder from the bottle mouth, the support device moves toward the fixed ring, so that the movable rings on the central axis are close to each other, and drive the anode sheet to expand and bend outward, so that the anode sheet group is "lantern-shaped", so that the area ratio of the cathode to the anode is 1.5-2.0:1.

[0043] Example 1

[0044] Surface treatment of the inner wall of the gas cylinder, material: 9100QP.

[0045] 1. Preparation of solution

[0046] Preparation of nickel-cobalt solution:

[0047] Main raw materials: nickel sulfate, cobalt sulfate, citric acid, boric acid, slotting additives. Preparation process: Add 70% pure water according to the amount of solution, heat to 55 ° C, add boric acid, citric acid, nickel sulfate, cobalt sulfate in sequence to dissolve, after dissolution is complete, adjust the volume to the standard volume and stir evenly; solution electrolysis: use 1A / dm 2 Electrolyze for more than 12 hours at a current density of 1000 nm until the coating on the cathode plate turns brown instead of black; adjust the pH with nickel carbonate, add deionized water to the usable range, and then test plating.

[0048] Preparation of tungsten alloy solution:

[0049] Main raw materials: nickel sulfate, sodium tungstate, phosphorous acid, citric acid, sodium citrate, slotting additive. Preparation process: Add 70% pure water according to the prepared solution volume, heat to 55°C, add citric acid, sodium citrate, sodium tungstate, phosphorous acid, and nickel sulfate in order to dissolve, stir, adjust the pH with ammonia, add deionized water to the working range, and then test plate.

[0050] 2. Pretreatment of plated parts

[0051] Internal wall sandblasting, chemical degreasing and electrolytic degreasing.

[0052] 3. Workpiece activation

[0053] The inner wall of the pretreated gas cylinder is washed with hot water and cold water in sequence, and then electro-activated (nitrate) (sodium nitrate solution, concentration: 400g / L) for 15 minutes, and then chemically activated (dilute sulfuric acid, mass fraction: 10%) for 10 minutes. After activation is completed, it is washed with tap water and deionized water.

[0054] 4. Plating

[0055] Electroplating of nickel-cobalt coating and tungsten alloy coating is carried out in sequence. When electroplating the nickel-cobalt coating, a pictographic anode made of titanium-iridium coated metal oxide is used. Three groups of anode sheet groups are arranged axially around the central conductive axis. The pictographic anode is introduced into the gas cylinder from the mouth of the gas cylinder. The anode sheet is controlled to expand outward using a support device to make the anode sheet group "lantern-shaped". The area ratio of the cathode to the anode is 1.75:1. The width of the anode sheet used is 20 mm. Electroplating is carried out after the nickel-cobalt electroplating solution is passed through. The components of the nickel-cobalt electroplating solution are: nickel sulfate: 360 g / L, cobalt sulfate: 50 g / L, citric acid: 20 g / L, boric acid: 30 g / L. At a current density of 3 A / dm 2 , pH=4.0, temperature at 55℃, electroplating time: 120 minutes.

[0056] When electroplating tungsten alloy coating, a stainless steel anode is used. Three groups of anode sheets are arranged axially around the central conductive axis. The anode sheet is inserted into the gas cylinder through the cylinder mouth. The anode sheet is expanded outward using a spreading device to make the anode sheet group "lantern-shaped". The area ratio of cathode to anode is 1.75:1. The composition of the electroplating tungsten alloy solution is: nickel sulfate: 17g / L, sodium tungstate: 30g / L, phosphorous acid: 27g / L, citric acid: 40g / L, sodium citrate: 40g / L; at a current density of 5A / dm 2 , pH=7.1, temperature at 65℃, electroplating time: 60 minutes. After electroplating, rinse with deionized water for 10 minutes and blow dry.

[0057] During the two electroplating processes, air stirring was performed at the bottom, and the intensity parameter of the air stirring was controlled to be: 0.6m 3 / (min·m 2 );

[0058] In addition, the flow rate of electroplating solution A and electroplating solution B entering from the lower box inlet and flowing out from the upper box overflow port is controlled to be 185L / min.

[0059] 5. Hydrogen removal

[0060] After the electroplating was completed, dehydrogenation was performed at 200°C for 4.0 hours.

[0061] 6. Inspection

[0062] First, the coating is inspected visually. The coating surface is uniform, fine, smooth and continuous. Then, the microstructure is inspected. Figure 3 、 Figure 4 The coating is primarily composed of nickel-cobalt and tungsten alloy layers, with an average thickness of 45 μm for the nickel-cobalt layer and 14 μm for the tungsten alloy layer. The total coating thickness and the ratio of individual layer thicknesses generally meet the test design requirements, and the overall distribution is relatively uniform, indicating a relatively stable coating process. A roughness tester measured no more than Ra 0.8 μm. A neutral salt spray test revealed no rust after 1500 hours, and a surface hardness of 760 HV. Furthermore, the inner wall fatigue test cycle exceeded 1100 cycles, demonstrating that the inner surface coating meets the requirements for expansion and contraction during compressed air filling and discharging. The test was conducted in accordance with GB / T 9252-2017, "Fatigue Test Methods for Gas Cylinders."

[0063] The coating was tested for composition using a scanning electron microscope and energy dispersive spectrometer. The results showed that the nickel content in the nickel-cobalt coating was 88.45wt%, the cobalt content was 10.44wt%, and the remainder was inevitable impurities such as zinc and copper. The tungsten alloy coating contained 19.67wt% tungsten, 78.27wt% nickel, and 1.5wt% phosphorus. The remainder was inevitable impurities such as iron and copper. The testing was conducted in accordance with GB / T17359-2023.

[0064] Example 2

[0065] Surface treatment of the inner wall of the gas cylinder, material: 9100QP.

[0066] Preparation of nickel-cobalt solution:

[0067] Main raw materials: nickel sulfate, cobalt sulfate, citric acid, boric acid, slotting additives. Preparation process: Add 70% pure water according to the amount of solution, heat to 55 ° C, add boric acid, citric acid, nickel sulfate, cobalt sulfate in sequence to dissolve, after dissolution is complete, adjust the volume to the standard volume and stir evenly; solution electrolysis: use 1A / dm 2 Electrolyze for more than 12 hours at a current density of 1000 nm until the coating on the cathode plate turns brown instead of black; adjust the pH with nickel carbonate, add deionized water to the usable range, and then test plating.

[0068] Preparation of tungsten alloy solution:

[0069] Main raw materials: nickel sulfate, sodium tungstate, phosphorous acid, citric acid, sodium citrate, slotting additive. Preparation process: Add 70% pure water according to the prepared solution volume, heat to 55°C, add citric acid, sodium citrate, sodium tungstate, phosphorous acid, and nickel sulfate in order to dissolve, stir, adjust the pH with ammonia, add deionized water to the working range, and then test plate.

[0070] 2. Pretreatment of plated parts

[0071] Internal wall sandblasting, chemical degreasing and electrolytic degreasing.

[0072] 3. Workpiece activation

[0073] The inner wall of the pretreated gas cylinder was washed with hot water and cold water in sequence, and then electro-activated (sodium nitrate solution, concentration: 400g / L) for 15 minutes, and then chemically activated (dilute sulfuric acid solution, mass fraction: 10%) for 10 minutes. After activation, it was washed with tap water and deionized water.

[0074] 4. Plating

[0075] Electroplating of nickel-cobalt coating and tungsten alloy coating is carried out in sequence. When electroplating the nickel-cobalt coating, a pictographic anode made of titanium-iridium coated metal oxide is used. Three groups of anode sheets are arranged axially around the central conductive axis. The pictographic anode is introduced into the gas cylinder from the cylinder mouth. The anode sheet is controlled to expand outward by a support device to make the anode sheet group "lantern-shaped". The area ratio of the cathode to the anode is 1.75:1. Electroplating is carried out after the nickel-cobalt electroplating solution is introduced. The components of the nickel-cobalt electroplating solution are: nickel sulfate: 360g / L, cobalt sulfate: 50g / L, citric acid: 20g / L, boric acid: 30g / L. At a current density of 2A / dm 2 , using titanium-iridium coated metal oxide anode, pH = 4.0, temperature at 55 ° C, electroplating time: 120 minutes, after the electroplating is completed, directly enter the next process.

[0076] When electroplating tungsten alloy, a pictographic anode made of titanium-iridium coated metal oxide is used. Three groups of anode sheets are arranged axially around the central conductive axis. The pictographic anode is inserted into the gas cylinder through the cylinder mouth. The anode sheet is controlled to expand outward using a spreading device to make the anode sheet group "lantern-shaped". The area ratio of the cathode to the anode is 1.75:1. The components of the electroplating tungsten alloy solution are: nickel sulfate: 17g / L, sodium tungstate: 30g / L, phosphorous acid: 27g / L, citric acid: 40g / L, sodium citrate: 40g / L. At a current density of 5A / dm 2 , using titanium-iridium coated metal oxide anode, pH = 7.1, temperature between 70 ° C, electroplating time: 60 minutes. After electroplating is completed, rinse with deionized water for 10 minutes and blow dry.

[0077] During the two electroplating processes, air stirring was performed at the bottom, and the intensity parameter of the air stirring was controlled to be: 0.6m 3 / (min·m 2 );

[0078] In addition, the flow rate of electroplating solution A and electroplating solution B entering from the lower box inlet and flowing out from the upper box overflow port is controlled to be 185L / min.

[0079] 5. Hydrogen removal

[0080] After the electroplating was completed, dehydrogenation was performed at 200°C for 4.0 hours.

[0081] Example 3

[0082] Surface treatment of the inner wall of the gas cylinder, material: 9100QP.

[0083] Preparation of nickel-cobalt solution:

[0084] Main raw materials: nickel sulfate, cobalt sulfate, citric acid, boric acid, slotting additives. Preparation process: Add 70% pure water according to the amount of solution, heat to 55 ° C, add boric acid, citric acid, nickel sulfate, cobalt sulfate in sequence to dissolve, after dissolution is complete, adjust the volume to the standard volume and stir evenly; solution electrolysis: use 1A / dm 2 Electrolyze for more than 12 hours at a current density of 1000 nm until the coating on the cathode plate turns brown instead of black; adjust the pH with nickel carbonate, add deionized water to the usable range, and then test plating.

[0085] Preparation of tungsten alloy solution:

[0086] Main raw materials: nickel sulfate, sodium tungstate, phosphorous acid, citric acid, sodium citrate, slotting additive. Preparation process: Add 70% pure water according to the prepared solution volume, heat to 55°C, add citric acid, sodium citrate, sodium tungstate, phosphorous acid, and nickel sulfate in order to dissolve, stir, adjust the pH with ammonia, add deionized water to the working range, and then test plate.

[0087] 2. Pretreatment of plated parts

[0088] Internal wall sandblasting, chemical degreasing and electrolytic degreasing.

[0089] 3. Workpiece activation

[0090] The inner wall of the pretreated gas cylinder was washed with hot water and cold water in sequence, and then electro-activated (sodium nitrate solution, concentration: 400g / L) for 15 minutes, and then chemically activated (dilute sulfuric acid solution, mass fraction: 10%) for 10 minutes. After activation, it was washed with tap water and deionized water.

[0091] 4. Plating

[0092] Electroplating of nickel-cobalt coating and tungsten alloy coating is carried out in sequence. When electroplating the nickel-cobalt coating, a pictographic anode made of titanium-iridium coated metal oxide is used. Three groups of anode sheets are arranged axially around the central conductive axis. The pictographic anode is introduced into the gas cylinder from the mouth of the gas cylinder. The anode sheet is controlled to expand outward by a support device to make the anode sheet group "lantern-shaped". The area ratio of the cathode to the anode is 1.75:1. After the nickel-cobalt electroplating solution is introduced, electroplating is carried out. The components of the nickel-cobalt electroplating solution are: nickel sulfate: 360g / L, cobalt sulfate: 50g / L, citric acid: 20g / L, boric acid: 30g / L. At a current density of 3A / dm 2 , using titanium-iridium coated metal oxide anode, pH = 4.0, temperature at 60 ° C, electroplating time: 120 minutes, after the electroplating is completed, directly enter the next process.

[0093] When electroplating tungsten alloy coating, a pictographic anode made of titanium-iridium coated metal oxide is used. Three groups of anode sheets are arranged axially around the central conductive axis. The pictographic anode is inserted into the gas cylinder through the cylinder mouth. The anode sheet is controlled to expand outward using a spreading device to make the anode sheet group "lantern-shaped". The area ratio of the cathode to the anode is 1.75:1. After the tungsten alloy electroplating solution is introduced, electroplating is carried out. The components of the tungsten alloy electroplating solution are: nickel sulfate: 17g / L, sodium tungstate: 30g / L, phosphorous acid: 27g / L, citric acid: 40g / L, sodium citrate: 40g / L. At a current density of 7A / dm 2 , using titanium-iridium coated metal oxide anode, pH = 7.1, temperature between 75 ° C, electroplating time: 60 minutes. After electroplating is completed, rinse with deionized water for 10 minutes and blow dry.

[0094] During the two electroplating processes, air stirring was performed at the bottom, and the intensity parameter of the air stirring was controlled to be: 0.6m 3 / (min·m 2 );

[0095] In addition, the flow rate of electroplating solution A and electroplating solution B entering from the lower box inlet and flowing out from the upper box overflow port is controlled to be 185L / min.

[0096] 5. Hydrogen removal

[0097] After the electroplating was completed, dehydrogenation was performed at 200°C for 4.0 hours.

[0098] Comparative Example 1

[0099] In Comparative Example 1, a single tungsten alloy electroplating process is used for electroplating.

[0100] ① Electroplating pretreatment is the same as in Example 1.

[0101] ②Electroplating tungsten alloy.

[0102] Preparation of tungsten alloy solution:

[0103] Main raw materials: nickel sulfate, sodium tungstate, phosphorous acid, citric acid, sodium citrate, slotting additive. Preparation process: Add 700% pure water according to the prepared solution volume, heat to 55°C, add citric acid, sodium citrate, sodium tungstate, phosphorous acid, and nickel sulfate in order to dissolve, stir, adjust the pH with ammonia, add deionized water to the working range, and then test plate.

[0104] Using stainless steel anode, 5A / dm 2 The electroplating was carried out at a current density of 65°C for 180 minutes. After electroplating, the substrate was rinsed with deionized water for 10 minutes and then dried.

[0105] ③ Hydrogen removal

[0106] After the electroplating was completed, dehydrogenation was performed at 200°C for 4.0 hours.

[0107] Comparative Example 2

[0108] Other conditions were the same as those in Example 1, except that air stirring was not performed. As a result, the density of the coating was greatly reduced, and the surface of the coating was not smooth and had a large number of nodules.

[0109] Comparative Example 3

[0110] All other conditions were the same as in Example 1, except that the anode sheets in the pictographic anode were not grouped. The length of a single anode sheet was approximately three times that of that in Example 1, ultimately forming a long, lantern-shaped anode when stretched. The results showed that the plating uniformity was weaker than in Example 1, with a thicker center and thinner ends. The specific thicknesses are shown in Table 1. The coating was thinner at the inlet and outlet ends of the gas cylinder and thicker in the center. Corrosion resistance was also poorer at the ends and better in the center.

[0111]

[0112] The corrosion resistance of the gas cylinder coatings of the embodiment and the comparative example was tested, and the performance results are shown in Table 2:

[0113]

[0114] The embodiments described are preferred implementations of the present invention, but the present invention is not limited to the above implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing a double-layer composite coating of nickel-cobalt / tungsten alloy electroplated on the inner wall of a gas cylinder, characterized by: A nickel-cobalt layer is first electroplated on the inner wall of the gas cylinder, and then a tungsten alloy layer is electroplated on the surface of the nickel-cobalt layer. When electroplating the nickel-cobalt layer and the tungsten alloy layer, a pictographic anode is used. The pictographic anode includes a central conductive shaft, on which is provided an expandable anode sheet and a spreading device for driving the anode sheet to expand outward. Before the anode sheet expands, the radial dimension of the pictographic anode is smaller than the diameter of the gas cylinder mouth. When the pictographic anode enters the gas cylinder through the gas cylinder mouth, the outward expansion of the anode sheet controls the area ratio of the cathode to the anode to be 1.5-2.0:1 when electroplating the nickel-cobalt layer and the tungsten alloy layer. The nickel-cobalt coating contains Ni and Co, wherein the mass fraction of Co in the nickel-cobalt coating is 8-12%, and the mass fraction of Ni is 88-91%; the tungsten alloy coating contains W, Ni, and P, wherein the mass fraction of W in the tungsten alloy coating is 12-30%, the mass fraction of Ni is 65-88%, and the mass fraction of P is 0.5-5%.

2. The method for preparing the electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder according to claim 1, characterized in that: The pictographic anode includes a central conductive shaft, and several anode sheet groups are arranged axially around the central conductive shaft. In the anode sheet group located at the top of the pictographic anode, a fixed ring is provided at the top and fixed on the central conductive shaft. The two ends of the remaining anode sheet groups and the bottom end of the anode sheet group located at the top of the pictographic anode are welded to the movable ring. An opening device is provided on the central conductive shaft away from the fixed ring. When the pictographic anode enters the gas cylinder from the bottle mouth, the opening device moves toward the fixed ring, so that the movable rings on the central axis move closer to each other, and drive the anode sheet to expand outward, causing the anode sheet group to be "lantern-shaped".

3. The method for preparing the electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder according to claim 2, characterized in that: The number of the anode plate groups is three; The width of the anode sheet is 15-25 mm; The material of the pictographic anode is selected from one of titanium ruthenium coating metal oxide, titanium iridium coating metal oxide, and stainless steel.

4. The method for preparing a double-layer electroplated nickel-cobalt / tungsten alloy composite coating on the inner wall of a gas cylinder according to any one of claims 1 to 3, characterized in that: First, the inner wall of the gas cylinder is pretreated in sequence: hot water washing, cold water washing, activation, tap water washing, deionized water washing, and then electroplating a layer of nickel-cobalt coating; The pretreatment is to sequentially perform sandblasting, chemical degreasing and electrolytic degreasing on the inner wall of the gas cylinder; The activation process is to sequentially perform electrical activation and chemical activation on the inner wall of the pretreated gas cylinder. The process of the electrical activation is to place the pretreated inner wall of the gas cylinder in a nitrate solution for electrical activation for 10-20 minutes. The concentration of the nitrate solution is 380-420g / L. The process of the chemical activation is to use a sulfuric acid solution with a mass fraction of 8-12% for activation for 5-10 minutes.

5. The method for preparing a double-layer electroplated nickel-cobalt / tungsten alloy composite coating on the inner wall of a gas cylinder according to any one of claims 1 to 3, characterized in that: The electroplating solution A for the nickel-cobalt electroplating layer comprises nickel sulfate: 340-380 g / L, cobalt sulfate: 40-55 g / L, citric acid: 15-25 g / L, and boric acid: 25-35 g / L. When the nickel-cobalt electroplating layer is applied, the current density is 1-10 A / dm 2 , temperature is 30-60℃, pH is 2.0-5.0; The electroplating solution B for the tungsten alloy coating comprises nickel sulfate: 14-22 g / L, sodium tungstate: 25-35 g / L, phosphorous acid: 20-30 g / L, citric acid: 30-180 g / L, and sodium citrate: 30-100 g / L. When the tungsten alloy coating is electroplated, the current density is 3-15 A / dm 2 , temperature is 50-80℃, pH is 5.0-8.

0.

6. The method for preparing a double-layer electroplated nickel-cobalt / tungsten alloy composite coating on the inner wall of a gas cylinder according to any one of claims 1 to 3, characterized in that: During the electroplating of the nickel-cobalt coating and the tungsten alloy coating, the gas cylinder is vertically fixed on the bracket.

7. The method for preparing the electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder according to claim 6, characterized in that: An upper box body is provided at the upper end of the gas cylinder, and a lower box body is provided at the lower end. When the nickel-cobalt plating layer and the tungsten alloy plating layer are electroplated, electroplating solution A and electroplating solution B enter from the inlet of the lower box body and flow out from the overflow port of the upper box body, forming a closed solution flow inside; the flow rate of the solution flow is ≥185L / min.

8. The method for preparing the electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder according to claim 6, characterized in that: During the electroplating of the nickel-cobalt coating and the tungsten alloy coating, the bottom of the cylinder is subjected to air stirring, and the intensity of the air stirring is 0.5-0.8m 3 / (min·m 2 ).

9. The electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder prepared by the preparation method according to any one of claims 1 to 3, characterized in that: The electroplated nickel-cobalt / tungsten alloy double-layer composite coating consists of a nickel-cobalt coating and a tungsten alloy coating from the inside to the outside; the thickness of the nickel-cobalt coating is 20-45 μm, and the thickness of the tungsten alloy coating is 10-20 μm.

10. Application of the electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder prepared by the preparation method according to any one of claims 1 to 3, characterized in that: Gas cylinders containing electroplated nickel-cobalt / tungsten alloy double-layer composite coatings are used in marine environments.

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