Pretreatment process for improving binding force and corrosion resistance of coating of hydraulic oil cylinder of coal machine

Abstract

The invention relates to the technical field of coal machine hydraulic oil cylinder electroplating machining, and particularly discloses a pretreatment process for improving the binding force and corrosion resistance of a coating of a coal machine hydraulic oil cylinder. According to the method, the micro-etching procedure is embedded into the traditional pretreatment process of the coal machine hydraulic oil cylinder, the optimal procedure sequence of treatment is defined, a micro-etching liquid component and a parameter system matched with the coal machine hydraulic oil cylinder are obtained through optimization, accurate matching of the roughness variation and the coating performance is achieved, the application limitation of an existing micro-etching process on large parts is broken through, and the application range of the micro-etching process on the large parts is widened. The technical problem of microstructure reconstruction of the large hydraulic component is solved. And compared with a traditional process, on the premise that the equipment investment and the production complexity are not increased, the salt mist resistance time of the plating layer is greatly prolonged, and the plating layer binding force is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of electroplating technology, specifically relating to a pretreatment process for improving the adhesion and corrosion resistance of coatings on hydraulic cylinders of coal mining machinery. Background Technology

[0002] As a core actuator in coal mining equipment, the hydraulic cylinder of a coal mining machine operates for extended periods in the high-humidity, high-dust, and corrosive underground environment. The adhesion and corrosion resistance of its surface coating directly affect the operational safety and service life of the equipment. Currently, the mainstream pretreatment process in the industry is mechanical polishing + electrolytic degreasing + acid pickling and activation + electroplating. This process has the following technical shortcomings: After mechanical polishing, microscopic defects such as tiny protrusions, burrs, and grinding lines remain on the surface of the cylinder. At the same time, a thin oxide / passivation film is formed. Acid pickling and activation can only remove some surface impurities and cannot reconstruct the microstructure.

[0003] The coating and the substrate mainly rely on chemical bonding and lack an effective mechanical interlocking structure. Under the frequent reciprocating motion and corrosive environment downhole, the coating is prone to peeling and flaking.

[0004] After using existing processes, the corrosion resistance of the cylinder coating to salt spray is generally only about 152 hours, which is insufficient to meet the corrosion resistance requirements for long-term stable operation of coal mine equipment, resulting in increased cylinder maintenance frequency and higher operating costs.

[0005] In existing technologies, micro-etching has been applied to electroplating small parts such as electronic components to improve coating adhesion. However, for large, heavy-duty components like hydraulic cylinders in coal mining machinery, a suitable micro-etching process parameter system has not yet been established, nor is the optimal embedding position of the micro-etching step in traditional pretreatment processes clearly defined, making direct application impossible. Therefore, there is an urgent need to develop a dedicated micro-etching pretreatment process for hydraulic cylinders in coal mining machinery to solve the technical problems of weak coating adhesion and insufficient corrosion resistance in existing processes. Summary of the Invention

[0006] In view of the defects and problems of weak adhesion and insufficient corrosion resistance of the coating on the hydraulic cylinders of coal mining machinery, the present invention provides a pretreatment process to improve the adhesion and corrosion resistance of the coating on the hydraulic cylinders of coal mining machinery.

[0007] A pretreatment process for improving the adhesion and corrosion resistance of coatings on hydraulic cylinders of coal mining machinery includes the following steps: (1) After polishing and grinding the specimen, chemical degreasing is performed, followed by rinsing and drying. (2) Place the specimen treated in (1) into the micro-etching tank, pour in the micro-etching solution, connect the anode of the power supply, and the distance between the graphite electrode and one side of the specimen is 90-110 mm. Etch at a current density of 2-3 A / dm² and room temperature for 1.2-1.8 min. After taking it out, rinse it clean and dry it. (3) Place the specimen treated in (2) into the electrostatic descaling tank. The distance between the stainless steel electrode and the specimen on one side is 90-110 mm. Electrostatic descaling is performed at a current density of 5 A / dm² and 60±2℃ for 4-6 min. After removal, rinse and dry. (4) Immerse the specimen treated in (3) in 5% hydrochloric acid solution for 1 minute, then rinse and dry it. (5) The specimen treated in (4) was plated with copper-tin alloy at a current density of 2A / dm² and 60±2℃ for 70-100 min. After the plating was completed, the thickness was measured. (6) Polish and grind the specimen after (5) so that the coating thickness is 45-55μm and the roughness is within Ra0.4.

[0008] The above-mentioned pretreatment process for improving the adhesion and corrosion resistance of the coating of the hydraulic cylinder of the coal hoisting machine includes step (1) placing the specimen in a chemical degreasing tank, pouring in chemical degreasing solution, and degreasing for 5 min at 60±2℃; the chemical degreasing solution includes 10-30 g / L sodium hydroxide, 25-40 g / L sodium carbonate, and 30-50 g / L trisodium phosphate.

[0009] The above-mentioned pretreatment process for improving the adhesion and corrosion resistance of the coating of the hydraulic cylinder of the coal hoisting machine includes, in step (2), a micro-etching solution comprising 160 mL / L of 50% sulfuric acid by volume, 6-10 mL / L of etching additive and deionized water; the etching additive comprises 30-50% of sulfonate surfactant or nonionic surfactant, 15-30% of organic carboxylic acid corrosion inhibitor, 10-20% of complexing agent and 5-15% of stabilizer.

[0010] The pretreatment process for improving the adhesion and corrosion resistance of the coating on the hydraulic cylinder of the coal hoisting machine mentioned above includes a micro-etching solution that further comprises an inducing agent and a competing modifier. The inducing agent is any one of perylene tetracarboxylic acid diimide derivative, perylene tetracarboxylic acid dianhydride derivative, or benzobenzene derivative; the competing modifier is propynyl alcohol.

[0011] In the aforementioned pretreatment process for improving the adhesion and corrosion resistance of the coating on the hydraulic cylinder of the coal hoisting machine, the amount of the inducing agent added is 0.005-0.05%; and the amount of the competing modifier added is 0.001-0.01%.

[0012] In the aforementioned pretreatment process for improving the adhesion and corrosion resistance of the coating on the hydraulic cylinder of the coal hoisting machine, the organic carboxylic acid corrosion inhibitor is a citric acid derivative; the complexing agent is an amine compound; and the stabilizer is an alcohol derivative.

[0013] The above-mentioned pretreatment process for improving the adhesion and corrosion resistance of the coating of the hydraulic cylinder of the coal hoisting machine, in step (2), the distance between the graphite electrode and the specimen on one side is 100 mm, and the etching is carried out at a current density of 3 A / dm² and at room temperature for 1.5 min.

[0014] The above-mentioned pretreatment process for improving the bonding strength and corrosion resistance of the coating of the hydraulic cylinder of the coal hoisting machine, the polishing and grinding process in steps (1) and (6) is to polish with a 400-mesh flap wheel, and then successively use 600-mesh, 800-mesh, 1000-mesh and 1500-mesh sandpaper for grinding, with a rotation speed of 1500 r / min and grinding for 5 min.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention incorporates the micro-etching process into the traditional pretreatment process of coal mining machinery hydraulic cylinders, and places the micro-etching process between mechanical polishing and acid pickling activation. It also optimizes the composition of the micro-etching solution and the micro-etching parameter system to achieve a precise match between the roughness change and the coating performance. This breaks through the application limitations of existing micro-etching processes on large parts and solves the technical problem of micro-morphology reconstruction of large hydraulic components.

[0016] This invention incorporates a perylenetetracarboxylic acid diimide derivative as an inducer and a competing modulator, propynyl alcohol, into a micro-etching solution. In the acidic environment of the micro-etching solution, the inducer molecules are partially protonated and dispersed in the solution. When the acid corrodes the substrate metal, exposing fresh atomic layers, the inducer molecules, through van der Waals forces and possible weak coordination between their planar conjugated structure and specific crystal planes on the metal surface, rapidly and preferentially adsorb onto the metal, forming a template layer. Simultaneously, metal ions complexed by the complexing agent, during diffusion, are induced by this template and preferentially reduced or deposited on the template layer. The deposited metal... Atoms tend to follow the crystallographic guidance of the template to form tiny nuclei or redeposited layers with preferred orientations. This process dynamically competes with and occurs simultaneously with the corrosion process of the host, ultimately forming a composite micromorphology on the surface that is composed of oriented redeposited structures and moderate corrosion depressions, with periodic or directional characteristics. Meanwhile, propynyl alcohol diffuses faster than the inducing agent, and can temporarily occupy some highly active sites, optimizing the uniformity of inducing agent adsorption and avoiding local accumulation failure due to excessively rapid adsorption, so that the inducing agent template layer can be spread more uniformly and controllably.

[0017] This invention's processing technology achieves a balance between complete removal of the passivation layer and uniform reconstruction of the microstructure. The Rz variation of approximately 18% falls within the optimal range for anchoring effect and coating coverage, avoiding coating defects caused by insufficient etching due to low current density or excessive etching. The mechanical interlocking structure formed by micro-etching and the deposited layer synergistically enhances the surface activity of the subsequent acid pickling activation, significantly strengthening the coating adhesion. Simultaneously, the resulting uniform microstructure ensures more complete coating coverage, reducing porosity and entry points for corrosive media, and extending the salt spray corrosion failure time. Compared to traditional processes, this invention significantly improves the salt spray resistance and adhesion of the coating without increasing equipment investment or production complexity. Attached Figure Description

[0018] Figure 1 A comparison chart showing the average rust prevention time of hydraulic cylinders treated with different methods. Detailed Implementation

[0019] This invention provides a pretreatment process for electroplating of hydraulic cylinders used in coal mining machinery. By adding a micro-etching step between mechanical polishing and acid pickling activation, the microstructure is optimized and the coating adhesion mechanism is strengthened, achieving a simultaneous improvement in coating adhesion and corrosion resistance, and extending the service life of the cylinder in harsh underground environments. The invention will be further described below with reference to specific embodiments.

[0020] Example 1: This example provides a pretreatment process for improving the adhesion and corrosion resistance of the coating on a coal mining machinery hydraulic cylinder. Specifically, the process involves mechanical polishing → chemical degreasing → hot water washing → cold water washing → micro-etching → water washing (×2) → electrolytic descaling → water washing (×2) → acid pickling activation → water washing (×2) → copper-tin alloy plating → mechanical polishing. The test piece used is a 30CrMnSiA material test piece with dimensions of φ35mm×180mm, conforming to the cylinder substrate material standard. The micro-etching equipment consists of a miniature electroplating tank and a high-frequency switching power supply (model GGDFH 100A / +15V), equipped with a graphite anode. A precision roughness tester is used to measure Ra and Rz parameters, and a coating thickness gauge is used to determine the coating thickness.

[0021] The specific steps are as follows: (1) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then polish it with 600-grit, 800-grit and 1000-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness of the test bar. (2) Chemical degreasing: The polished test bar is placed in a chemical degreasing tank. The tank solution consists of 20 g / L sodium hydroxide, 35 g / L sodium carbonate, and 40 g / L trisodium phosphate. The tank temperature is 60±2℃ and the time is 5 min. After taking it out, rinse it with deionized water until there is no oil or degreasing solution residue on the surface. (3) Micro-etching treatment: After chemical degreasing, the specimen is placed in the micro-etching tank, the micro-etching solution is poured in, and the power supply anode is connected. The distance between the graphite anode and the specimen on one side is controlled to be 100 mm. The etching is started at a current density of 3 A / dm² and room temperature. After 1.5 min, it is taken out and rinsed with deionized water until there is no micro-etching solution residue on the surface. The micro-etching solution used includes: 160 mL / L sulfuric acid with a volume ratio of 50%, 6-10 mL / L etching additive and deionized water. The etching additive includes 40% sodium dodecylbenzenesulfonate, 25% citric acid derivative, 15% ethylenediamine, 10% propylene glycol, 0.05% perylenetetracarboxylic acid diimide derivative, 0.01% propynyl alcohol, and the remainder is deionized water. Sodium dodecylbenzenesulfonate mixed with sulfuric acid can reduce the surface tension of the tank solution, form a thin foam layer, inhibit the volatilization of sulfuric acid mist, improve the operating environment, and promote the wetting of the etching solution and the surface of the workpiece, avoiding uneven etching caused by local "dry areas". Citric acid, acting as a corrosion inhibitor, can adsorb onto the hardened steel surface, suppressing the over-corrosion of the substrate by sulfuric acid, preventing pitting and pinholes, achieving micro-etching rather than strong dissolution, and protecting the original surface quality of the substrate. Ethylenediamine, acting as a complexing agent, can react with the Fe produced during etching. 2+ / Fe 3+ The formation of stable complexes allows for the accumulation of iron impurities in the bath up to 20 g / L while maintaining a stable etching rate, thus extending the bath's lifespan. Propylene glycol, as a stabilizer, maintains stable bath viscosity, preventing sudden changes in etching rate due to temperature and sulfuric acid concentration fluctuations, thereby improving process tolerance. Perylenetetracarboxylic acid diimide, as an inducer, can rapidly and preferentially adsorb onto specific crystal planes of the metal surface through van der Waals forces and potential weak coordination, forming a template layer. Simultaneously, metal ions complexed by the complexing agent preferentially reduce or deposit on the template layer during diffusion, forming micro-nuclei or redeposition layers with preferred orientations. Propynol, as a competing modulator, diffuses faster than the inducer and can temporarily occupy some highly active sites, preventing localized accumulation failure due to excessively rapid adsorption, allowing the inducer template layer to spread more uniformly and controllably.

[0022] (4) Electrolytic descaling: Place the micro-etched specimen into the electrolytic descaling tank, connect the power supply anode, control the distance between the stainless steel anode and the specimen on one side to be 100mm, start the electrolytic descaling according to the parameters of current density 5A / dm² and 60±2℃, continue for 5min and then take it out, rinse with deionized water until there is no tank liquid residue on the surface. (5) Pickling activation: Immerse the specimen after electrolytic descaling in 5% hydrochloric acid solution and soak at room temperature for 1 minute. After taking it out, rinse it with deionized water until there is no acid residue on the surface. (6) Electroplating: The existing copper-tin alloy electroplating process is adopted. The plating is carried out for 80 minutes with a current density of 2A / dm² and a temperature of 60±2℃. After the electroplating is completed, the thickness is measured and polishing is performed.

[0023] (7) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then, polish it with 600-grit, 800-grit, 1000-grit and 1500-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness and thickness of the test bar. The coating thickness is controlled within 50 μm and the roughness is controlled within Ra0.4.

[0024] Example 2: A pretreatment process for improving the adhesion and corrosion resistance of a coating on a coal mining machinery hydraulic cylinder, the specific steps of which are as follows: (1) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then polish it with 600-grit, 800-grit and 1000-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness of the test bar. (2) Chemical degreasing: The polished test bar is placed in a chemical degreasing tank. The tank solution consists of sodium hydroxide, sodium carbonate, and trisodium phosphate. The tank temperature is 60±2℃ and the time is 5min. After taking it out, rinse it with deionized water until there is no oil stain or degreasing solution residue on the surface. (3) Micro-etching treatment: The chemically degreased specimen was placed in the micro-etching tank. The micro-etching solution was the same as in Example 1. The power supply anode was connected, and the distance between the graphite anode and the specimen on one side was controlled to be 100 mm. Etching was started at a current density of 3 A / dm² and room temperature. After 1 min, the specimen was taken out and rinsed with deionized water until there was no micro-etching solution residue on the surface. (4) Electrolytic descaling: Place the micro-etched specimen into the electrolytic descaling tank, connect the power supply anode, control the distance between the stainless steel anode and the specimen on one side to be 100mm, start the electrolytic descaling according to the parameters of current density 5A / dm² and 60±2℃, continue for 5min and then take it out, rinse with deionized water until there is no tank liquid residue on the surface. (5) Pickling activation: Immerse the specimen after electrolytic descaling in 5% hydrochloric acid solution and soak at room temperature for 1 minute. After taking it out, rinse it with deionized water until there is no acid residue on the surface. (6) Electroplating: The existing copper-tin alloy electroplating process is adopted. The plating is carried out for 80 minutes with a current density of 2A / dm² and a temperature of 60±2℃. After the electroplating is completed, the thickness is measured and polishing is performed.

[0025] (7) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then, polish it with 600-grit, 800-grit, 1000-grit and 1500-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness and thickness of the test bar. The coating thickness is controlled within 50 μm and the roughness is controlled within Ra0.4.

[0026] Example 3: A pretreatment process for improving the adhesion and corrosion resistance of a coating on a coal mining machinery hydraulic cylinder, the specific steps of which are as follows: (1) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then polish it with 600-grit, 800-grit and 1000-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness of the test bar. (2) Chemical degreasing: The polished test bar is placed in a chemical degreasing tank. The tank solution consists of sodium hydroxide, sodium carbonate, and trisodium phosphate. The tank temperature is 60±2℃ and the time is 5min. After taking it out, rinse it with deionized water until there is no oil stain or degreasing solution residue on the surface. (3) Micro-etching treatment: The chemically degreased specimen was placed in the micro-etching tank. The micro-etching solution was the same as in Example 1. The power supply anode was connected, and the distance between the graphite anode and the specimen on one side was controlled to be 100 mm. The etching was started with the parameters of current density 2A / dm² and room temperature. After 1 min, it was taken out and rinsed with deionized water until there was no micro-etching solution residue on the surface. (4) Electrolytic descaling: Place the micro-etched specimen into the electrolytic descaling tank, connect the power supply anode, control the distance between the stainless steel anode and the specimen on one side to be 100mm, start the electrolytic descaling according to the parameters of current density 5A / dm² and 60±2℃, continue for 5min and then take it out, rinse with deionized water until there is no tank liquid residue on the surface. (5) Pickling activation: Immerse the specimen after electrolytic descaling in 5% hydrochloric acid solution and soak at room temperature for 1 minute. After taking it out, rinse it with deionized water until there is no acid residue on the surface. (6) Electroplating: The existing copper-tin alloy electroplating process is adopted. The plating is carried out for 80 minutes with a current density of 2A / dm² and a temperature of 60±2℃. After the electroplating is completed, the thickness is measured and polishing is performed.

[0027] (7) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then, polish it with 600-grit, 800-grit, 1000-grit and 1500-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness and thickness of the test bar. The coating thickness is controlled within 50 μm and the roughness is controlled within Ra0.4.

[0028] Example 4: A pretreatment process for improving the adhesion and corrosion resistance of a coating on a coal mining machinery hydraulic cylinder, the specific steps of which are as follows: (1) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then polish it with 600-grit, 800-grit and 1000-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness of the test bar. (2) Chemical degreasing: The polished test bar is placed in a chemical degreasing tank. The tank solution consists of sodium hydroxide, sodium carbonate, and trisodium phosphate. The tank temperature is 60±2℃ and the time is 5min. After taking it out, rinse it with deionized water until there is no oil stain or degreasing solution residue on the surface. (3) Micro-etching treatment: The chemically degreased specimen was placed in the micro-etching tank. The micro-etching solution was the same as in Example 1. The power supply anode was connected, and the distance between the graphite anode and the specimen on one side was controlled to be 100 mm. The etching was started with the parameters of current density 2A / dm² and room temperature. After 1.5 min, it was taken out and rinsed with deionized water until there was no micro-etching solution residue on the surface. (4) Electrolytic descaling: Place the micro-etched specimen into the electrolytic descaling tank, connect the power supply anode, control the distance between the stainless steel anode and the specimen on one side to be 100mm, start the electrolytic descaling according to the parameters of current density 5A / dm² and 60±2℃, continue for 5min and then take it out, rinse with deionized water until there is no tank liquid residue on the surface. (5) Pickling activation: Immerse the specimen after electrolytic descaling in 5% hydrochloric acid solution and soak at room temperature for 1 minute. After taking it out, rinse it with deionized water until there is no acid residue on the surface. (6) Electroplating: The existing copper-tin alloy electroplating process is adopted. The plating is carried out for 80 minutes with a current density of 2A / dm² and a temperature of 60±2℃. After the electroplating is completed, the thickness is measured and polishing is performed.

[0029] (7) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then, polish it with 600-grit, 800-grit, 1000-grit and 1500-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness and thickness of the test bar. The coating thickness is controlled within 50 μm and the roughness is controlled within Ra0.4.

[0030] Comparative Example 1: A pretreatment process for improving the adhesion and corrosion resistance of a coating on a coal mining machinery hydraulic cylinder, the specific steps of which are as follows: (1) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then polish it with 600-grit, 800-grit and 1000-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness of the test bar. (2) Chemical degreasing: The polished test bar is placed in a chemical degreasing tank. The tank solution consists of 20 g / L sodium hydroxide, 35 g / L sodium carbonate, and 40 g / L trisodium phosphate. The tank temperature is 60±2℃ and the time is 5 min. After taking it out, rinse it with deionized water until there is no oil or degreasing solution residue on the surface. (3) Micro-etching treatment: The chemically degreased specimen was placed in the micro-etching tank, the micro-etching solution was poured in, and the power supply anode was connected. The distance between the graphite anode and the specimen on one side was controlled to be 100 mm. The etching was started at a current density of 3 A / dm² and room temperature. After 1.5 min, the specimen was taken out and rinsed with deionized water until there was no micro-etching solution residue on the surface. The micro-etching solution used included: 160 mL / L sulfuric acid with a volume ratio of 50%, 6-10 mL / L etching additive and deionized water. The etching additive included 40% sodium dodecylbenzenesulfonate, 25% citric acid derivative, 15% ethylenediamine and 10% propylene glycol.

[0031] (4) Electrolytic descaling: Place the micro-etched specimen into the electrolytic descaling tank, connect the power supply anode, control the distance between the stainless steel anode and the specimen on one side to be 100mm, start the electrolytic descaling according to the parameters of current density 5A / dm² and 60±2℃, continue for 5min and then take it out, rinse with deionized water until there is no tank liquid residue on the surface. (5) Pickling activation: Immerse the specimen after electrolytic descaling in 5% hydrochloric acid solution and soak at room temperature for 1 minute. After taking it out, rinse it with deionized water until there is no acid residue on the surface. (6) Electroplating: The existing copper-tin alloy electroplating process is adopted. The plating is carried out for 80 minutes with a current density of 2A / dm² and a temperature of 60±2℃. After the electroplating is completed, the thickness is measured and polishing is performed.

[0032] (7) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then, polish it with 600-grit, 800-grit, 1000-grit and 1500-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness and thickness of the test bar. The coating thickness is controlled within 50 μm and the roughness is controlled within Ra0.4.

[0033] Comparative Example 2: A pretreatment process for a coal mining machinery hydraulic cylinder, the specific steps of which are as follows: (1) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-grit flap wheel. Then polish it with 600-grit, 800-grit and 1000-grit sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness of the test bar. (2) Chemical degreasing: The polished test bar is placed in a chemical degreasing tank. The tank solution consists of sodium hydroxide, sodium carbonate, and trisodium phosphate. The tank temperature is 60±2℃ and the time is 5min. After taking it out, rinse it with deionized water until there is no oil stain or degreasing solution residue on the surface. (3) Pickling and activation: Immerse the chemically degreased specimen in a 5% hydrochloric acid solution for 1 minute at room temperature, then rinse with deionized water until no acid residue remains on the surface; (4) Electroplating: The existing copper-tin alloy electroplating process is adopted. The plating is carried out for 80 minutes with a current density of 2A / dm² and a temperature of 60±2℃. After the electroplating is completed, the thickness is measured and polishing is performed.

[0034] (5) Mechanical polishing: Fix the test bar on a polishing lathe and polish it with a 400-mesh flap wheel. Then, polish it with 600-mesh, 800-mesh, 1000-mesh and 1500-mesh sandpaper in sequence. The rotation speed is 1500 r / min and the polishing time is 5 min. After processing, check the roughness and thickness of the test bar. The coating thickness is controlled within 50 μm and the roughness is controlled within Ra0.4.

[0035] Experimental examples: Ra and Rz parameters were measured using a precision roughness tester; coating thickness was measured using a coating thickness gauge; acidic salt spray test was conducted using a salt spray test chamber; and coating adhesion test was conducted using a far-infrared high-temperature oven.

[0036] (1) The results of the surface roughness variation of the specimen are shown in Table 1 below.

[0037] Table 1. Surface roughness test results of specimens after different treatment processes

[0038] As shown in Table 1, the surface roughness parameters of all groups of specimens changed significantly after micro-etching treatment compared to before treatment. Among them, the surface roughness parameters of specimens with a roughness of 3A / dm changed significantly. 2 The average change in Rz of the micro-etching parameters over 1.5 min is about 18%, forming a uniform micro-peak-valley structure. This achieves a balance between complete removal of the passivation layer and uniform reconstruction of the micro-morphology, indicating that the average change in Rz is within the optimal range of anchoring effect and coating coverage. This ensures sufficient coating anchoring points and avoids coating defects caused by insufficient etching due to low current density and excessive etching.

[0039] (2) The corrosion resistance test (acidic salt spray test) results are shown in Table 2 below, and the average rust prevention time is as follows: Figure 1 As shown.

[0040] Table 2. Test results of corrosion resistance of different treatment groups

[0041] As can be seen from the acidic salt spray test results in Table 2, the pretreatment process of this invention can significantly improve the rust prevention time compared with the traditional process. The uniform microstructure makes the coating coverage more complete, reduces the porosity and penetration points of corrosive media, and prolongs the salt spray corrosion failure time. Among them, the specimens of Example 1 with micro-etching parameters of 3A / dm²×1.5min showed the best corrosion resistance, indicating that the micro-etching parameter treatment can significantly improve the corrosion resistance of the specimens.

[0042] (3) Coating adhesion test The thermal shock method was used for testing (the test piece was placed in a far-infrared high-temperature oven and heated to 300°C for 1 hour, then quickly removed and cooled in cold water, and the coating was observed to see if it peeled off or blistered).

[0043] Repeat the above steps to conduct multiple rounds of cyclic thermal shock tests and observe the adhesion of the coating. The results are shown in Table 3 below.

[0044] Table 3. Test results of coating adhesion of specimens in different treatment groups

[0045] As shown in Table 3, adding a micro-etching process to the traditional electroplating process can significantly improve the coating adhesion. The mechanical interlocking structure formed by micro-etching and the subsequent surface activity enhancement by acid pickling and activation have a synergistic effect, which significantly strengthens the coating adhesion. The coating adhesion of the specimens with micro-etching parameters of 3A / dm²×1.5min is significantly better.

[0046] In summary, the results indicate that adding a micro-etching process can significantly improve coating adhesion and corrosion resistance. The specimens using micro-etching parameters of 3 A / dm² × 1.5 min showed significantly better corrosion resistance and coating adhesion. Under the same micro-etching solution and etching time, using 3 A / dm²... 2 The average rust prevention time of the micro-etching current density is higher than 3A / dm. 2 The higher current density in the first treatment group allows for more complete dissolution of surface micro-protrusions, resulting in a more complex anchoring structure, stronger mechanical adhesion between the coating and the substrate, and reduced coating detachment in salt spray, thus extending the rust prevention time. Under the same micro-etching solution and current density, the coating in the 1.5-minute etching group exhibits higher corrosion resistance because appropriately extending the etching time (1.5 minutes) allows for more thorough removal of the surface passivation layer, more uniform microstructure, and more complete coating coverage, reducing the entry points for Cl⁻ in the salt spray (such as pores and bonding defects). Under the same micro-etching current density and etching time, the coatings in the treatment groups with added inducing agents and competing modifiers show significantly higher corrosion resistance.

[0047] The above description is only a preferred embodiment of the present invention and does not limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pretreatment process for improving the adhesion and corrosion resistance of coatings on hydraulic cylinders of coal mining machinery, characterized in that: Includes the following steps: (1) After polishing and grinding the specimen, chemical degreasing is performed, followed by rinsing and drying. (2) Place the specimen treated in (1) into the micro-etching tank, pour in the micro-etching solution, connect the anode of the power supply, and the distance between the graphite electrode and one side of the specimen is 90-110 mm. Etch at a current density of 2-3 A / dm² and room temperature for 1.2-1.8 min. After taking it out, rinse it clean and dry it. (3) Place the specimen treated in (2) into the electrostatic descaling tank. The distance between the stainless steel electrode and the specimen on one side is 90-110 mm. Electrostatic descaling is performed at a current density of 5 A / dm² and 60±2℃ for 4-6 min. After removal, rinse and dry. (4) Immerse the specimen treated in (3) in 5% hydrochloric acid solution for 1 minute, then rinse and dry it. (5) The specimen treated in (4) was plated with copper-tin alloy at a current density of 2A / dm² and 60±2℃ for 70-100 min. After the plating was completed, the thickness was measured. (6) Polish and grind the specimen after (5) so that the coating thickness is 45-55μm and the roughness is within Ra0.

4.

2. The pretreatment process for improving the adhesion and corrosion resistance of the coating on the hydraulic cylinder of a coal hoisting machine according to claim 1, characterized in that: In step (1), the specimen is placed in a chemical degreasing tank, and a chemical degreasing solution is poured in. The degreasing is carried out at 60±2℃ for 5 minutes. The chemical degreasing solution includes sodium hydroxide 10-30 g / L, sodium carbonate 25-40 g / L, and trisodium phosphate 30-50 g / L.

3. The pretreatment process for improving the adhesion and corrosion resistance of the coating on the hydraulic cylinder of the coal hoisting machine according to claim 1, characterized in that: The micro-etching solution in step (2) includes 160 mL / L of 50% sulfuric acid by volume, 6-10 mL / L of etching additive and deionized water; the etching additive consists of 30-50% sulfonate surfactant or nonionic surfactant, 15-30% organic carboxylic acid corrosion inhibitor, 10-20% complexing agent and 5-15% stabilizer.

4. The pretreatment process for improving the adhesion and corrosion resistance of the coating on the hydraulic cylinder of the coal hoisting machine according to claim 3, characterized in that: The organic carboxylic acid corrosion inhibitor is a citric acid derivative; the complexing agent is an amine compound; and the stabilizer is an alcohol derivative.

5. The pretreatment process for improving the adhesion and corrosion resistance of the coating on the hydraulic cylinder of a coal hoisting machine according to claim 1, characterized in that: In step (2), the distance between the graphite electrode and one side of the specimen is 100 mm, and the etching is performed at a current density of 3 A / dm² and at room temperature for 1.5 min.

6. The pretreatment process for improving the adhesion and corrosion resistance of the coating on the hydraulic cylinder of a coal hoisting machine according to claim 1, characterized in that: In steps (1) and (6), the polishing and grinding process involves polishing with a 400-grit flap wheel, followed by grinding with 600-grit, 800-grit, 1000-grit, and 1500-grit sandpaper in sequence, at a speed of 1500 r / min for 5 min.

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