Gate valve outer surface treatment process

Abstract

The invention provides a gate valve outer surface treatment process, and relates to the technical field of surface coating, according to the process, 80-120-mesh quartz sand is subjected to 0.4-0.6 MPa sand blasting pretreatment to enable the surface roughness Ra to reach 6.3-12.5 microns, epoxy resin and a curing agent are mixed according to the ratio of (3-5): 1, 5-8% of nano AlO particles and 2-4% of graphene nanosheets are added, a 150-200 microns wet film is formed through high-pressure airless spraying, and the surface roughness Ra of the gate valve is controlled to be 6.3-12.5 microns. And after segmented curing at 120-150 DEG C, the surface is strengthened through plasma treatment. According to the technology, parameters such as the sand grain speed and the nano-particle adding amount are accurately controlled through a formula, the average thickness of the coating is larger than or equal to 200 microns, the adhesive force reaches the ISO0 level, 5% NaCl salt mist resistance is larger than or equal to 1000 h, the pencil hardness is larger than or equal to 2 H, the problems that a traditional technology is poor in adhesive force and insufficient in corrosion resistance are solved, and efficient protection of the outer surface of the gate valve is achieved. Process parameters and coating performance are quantitatively associated through a sand blasting speed formula, a nano-particle adding amount formula and a dry and wet film thickness conversion model, the sand blasting speed is controlled to be 30-50 m / s, the dry film thickness precision is + / -10 microns, and stress cracks of the coating are avoided by combining a PLC segmented heating curing technology.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of surface coating, and more particularly relates to a gate valve outer surface treatment process. BACKGROUND

[0002] In industrial pipeline systems, as a key component for controlling fluid on-off, the outer surface of the gate valve is long-term exposed to corrosive media, mechanical wear and other harsh environments, and the surface protection performance directly affects the equipment life and operation safety. The current gate valve outer surface treatment process mainly has the following technical bottlenecks:

[0003] Traditional treatment processes such as coating ordinary paint or hot dip galvanizing, although low in cost, have insufficient bonding strength between the coating and the substrate, and are prone to peeling under conditions such as vibration and temperature change. For example, the adhesion of an epoxy resin coating using air spraying can only reach level 2-3 of ISO2409 standard, and rusting occurs after 300 hours of salt spray testing, which cannot meet the protection requirements of harsh scenes such as petroleum and chemical industry.

[0004] The existing process lacks precision control of surface pretreatment. Most enterprises use manual polishing or low-pressure sandblasting, and the surface roughness has great randomness, with a Ra value fluctuation range of 25-50 μm, resulting in uneven coating thickness and weak bonding force in local areas, which becomes a corrosion breakthrough. Test data from a valve factory show that the early failure probability of gate valves without precise control of pretreatment parameters is more than 40% higher than that of standard treatment pieces.

[0005] The performance of the coating material is obviously limited. Traditional coatings lack nanoscale reinforcing phases, and the hardness is generally lower than 2H, which can be easily scratched during handling or installation, forming a corrosion channel. Moreover, the existing process does not introduce two-dimensional materials such as graphene to construct a corrosion-resistant network, and the salt spray resistance of the coating is generally less than 500 hours, which cannot meet the long-term corrosion resistance requirements of marine engineering and underground pipeline networks.

[0006] Process parameters rely on experience control and lack of quantitative standards. For example, traditional curing processes mostly use room temperature natural drying or constant heating, which can easily cause stress concentration in the coating, and there is a micro-crack rate of 10-15% detected; the wet film thickness error in the spraying process exceeds 20%, resulting in uneven dry film thickness and large dispersion of protection performance.

[0007] With the increasing demand for valve reliability in high-end manufacturing, there is an urgent need for an outer surface treatment technology with high adhesion, corrosion and wear resistance, and controllable process. The deficiencies of existing technologies in nanocomposite coating preparation, parameterized process control and full-process quality assurance have become key factors restricting the service life of gate valves, and urgent breakthroughs are needed through systematic innovation. SUMMARY

[0008] To address the aforementioned technical problems, this invention provides a gate valve external surface treatment process.

[0009] A gate valve external surface treatment process includes the following steps:

[0010] S1: Pretreatment: Sandblast the outer surface of the gate valve with quartz sand of 80-120 mesh at a pressure of 0.4-0.6MPa until the surface roughness Ra reaches 6.3-12.5μm;

[0011] S2: Coating preparation: Mix epoxy resin and curing agent at a mass ratio of (3-5):1, add 5-8% of nano Al2O3 particles (particle size 50-100nm) in total, stir evenly to obtain coating material;

[0012] S3: Spraying construction: Using high-pressure airless spraying equipment, under the conditions of temperature 20-25℃ and humidity ≤60%, the coating material is sprayed onto the surface of the gate valve at a spraying pressure of 0.8-1.2MPa to form a wet film thickness of 150-200μm.

[0013] S4: Curing treatment: Place the sprayed gate valve in a constant temperature chamber and raise the temperature to 120-150℃ at a rate of 5-8℃ / min. Keep it at this temperature for 2-3 hours and then cool it to room temperature with the furnace.

[0014] S5: Inspection and Acceptance: The coating thickness is tested using an eddy current thickness gauge. The average thickness is required to be ≥200μm, and the coating must pass a 5% NaCl solution salt spray test for ≥1000h without rust.

[0015] Preferably, the sand particle velocity in step S1 is calculated using the following formula:

[0016] ;

[0017] Where P is the sandblasting pressure (MPa), ρ is the sand particle density (g / cm³), d is the sand particle size (mm), and D is the sandblasting pipe diameter (mm). The sand particle velocity is controlled within the range of 30-50m / s.

[0018] Preferably, the amount of nano-Al2O3 particles added in step S2 is determined by the following formula:

[0019] ;

[0020] Where m is the mass of nanoparticles (kg), m0 is the mass of epoxy resin (kg), and Ra is the surface roughness after pretreatment (μm), ensuring that the coating and substrate have a bonding strength ≥50MPa.

[0021] Preferably, the conversion relationship between the wet film thickness and the dry film thickness in step S3 of the spraying application satisfies: Where d_d_d represents the dry film thickness (μm), d_d_wet represents the wet film thickness (μm), and w represents the percentage of volatile matter in the coating material (%). w is controlled to be ≤15% to ensure the dry film thickness accuracy is ±10μm.

[0022] Preferably, the heating rate of the curing process in step S4 is controlled by a PLC program. When the temperature reaches 80°C, the heating rate is automatically adjusted to 3-5°C / min to avoid stress cracks inside the coating.

[0023] Preferably, before the sandblasting treatment in step S1, the gate valve is first immersed in a 5-10% NaOH solution at 60-80℃ for ultrasonic cleaning for 10-15 minutes to remove surface oil stains, and the ultrasonic frequency is controlled at 40-60kHz.

[0024] Preferably, the coating material in step S2 further includes 2-4% of graphene nanosheets (≤10 layers, 1-5 μm in diameter) to improve the corrosion resistance of the coating and extend the salt spray test time by more than 20%.

[0025] Preferably, during the inspection and acceptance in step S5, the coating adhesion is tested using the cross-cut test with a cross-cut spacing of 1 mm, achieving a rating of level 0 in the ISO2409 standard, and the coating surface has a pencil hardness ≥2H.

[0026] Preferably, in step S3, the nozzle orifice diameter of the spraying equipment is 0.8-1.2mm, and the spraying distance is controlled at 150-200mm to ensure that the coating surface uniformity error is ≤5%.

[0027] Preferably, the process also includes a post-processing step: the outer surface of the cured gate valve is treated with a plasma treatment device in an Ar atmosphere (pressure 10-30Pa) at a power of 30-50W for 5-10 minutes to further improve the density of the coating surface.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. Precise pretreatment enhances coating adhesion: By combining sandblasting with specific particle size quartz sand and pressure parameters, along with ultrasonic cleaning with NaOH solution, the surface roughness of the gate valve is precisely controlled between 6.3-12.5μm, forming a uniform rough surface. This significantly improves the mechanical bonding strength between the coating and the substrate. The adhesion can reach ISO2409 standard level 0 after cross-cut adhesion testing, preventing coating peeling.

[0030] 2. Enhanced comprehensive performance of nanocomposite coating: Nano-Al2O3 particles and graphene nanosheets are introduced into the epoxy resin-based coating. By utilizing the reinforcing effect of nanoparticles and the corrosion-resistant network structure of graphene, the coating can withstand salt spray test time of over 1000 hours and has a pencil hardness of ≥2H. Compared with traditional coatings, the wear resistance is improved by more than 30%, and the corrosion resistance is extended by 2-3 times.

[0031] 3. Precise control achieved through parametric process: By using the sandblasting speed formula, the nanoparticle addition formula, and the dry-wet film thickness conversion model, the process parameters are quantitatively correlated with the coating performance. The sandblasting speed is controlled at 30-50m / s, and the dry film thickness accuracy is ±10μm. Combined with PLC segmented heating and curing technology, stress cracks in the coating are avoided, and precise control of the entire process from pretreatment to curing is achieved.

[0032] 4. High-efficiency spraying and post-treatment improve quality stability: High-pressure airless spraying, combined with optimization of nozzle orifice diameter, spraying distance and pressure, ensures that the uniformity error of the wet film thickness of the coating is ≤5%; plasma post-treatment in an Ar atmosphere enhances the density of the coating surface, reduces porosity, further isolates corrosive media, and ensures the consistency of coating performance.

[0033] 5. A comprehensive testing system ensures reliability: A multi-dimensional testing standard covering thickness, adhesion, hardness, and salt spray testing has been established. The average coating thickness is ≥200μm, and the coating has passed the 1000-hour rust-free test with 5% NaCl solution. This forms a closed-loop quality control system from process to acceptance, meeting industrial-grade corrosion resistance requirements and extending the service life of gate valves. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall process of the present invention. Detailed Implementation

[0035] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0036] Please see Figure 1 This invention provides a gate valve external surface treatment process. This process involves a series of steps, including pretreatment of the gate valve surface, coating preparation, spraying, curing, and testing. Combined with specific process parameters and material ratios, a high-performance protective coating is formed on the gate valve's external surface, effectively improving its corrosion resistance, wear resistance, and service life. The process incorporates nanoparticles to enhance coating performance and utilizes precise formulas to control process parameters, ensuring accurate execution of each step and achieving high-quality treatment of the gate valve's external surface.

[0037] Specific process steps:

[0038] (a) Preprocessing:

[0039] The outer surface of the gate valve is sandblasted using quartz sand with a particle size of 80-120 mesh under a pressure of 0.4-0.6 MPa. The sand particle velocity during sandblasting is determined according to the formula... The calculation is performed, where P is the sandblasting pressure (MPa), ρ is the sand particle density (g / cm³), d is the sand particle size (mm), and D is the sandblasting pipe diameter (mm). The sand particle velocity is controlled within the range of 30-50 m / s until the surface roughness Ra reaches 6.3-12.5 μm. Before sandblasting, the gate valve is immersed in a 5-10% NaOH solution at 60-80℃ and ultrasonically cleaned for 10-15 minutes at an ultrasonic frequency controlled at 40-60 kHz to remove surface oil and provide a good foundation for subsequent coating adhesion.

[0040] (II) Coating Preparation:

[0041] Epoxy resin and curing agent are mixed at a mass ratio of (3-5):1, and 5-8% of nano-Al2O3 particles (particle size 50-100nm) are added. The amount of nano-Al2O3 particles added is determined by the formula... The formula is defined as follows: m is the mass of nanoparticles (kg), m0 is the mass of epoxy resin (kg), and Ra is the surface roughness after pretreatment (μm). If necessary, 2-4% of graphene nanosheets (≤10 layers, 1-5 μm in diameter) can be added, and the mixture is stirred evenly to obtain the coating material.

[0042] (III) Spraying application:

[0043] High-pressure airless spraying equipment is used. Under conditions of temperature 20-25℃ and humidity ≤60%, the nozzle orifice diameter of the spraying equipment is 0.8-1.2mm, the spraying distance is controlled at 150-200mm, and the coating material is sprayed onto the gate valve surface at a spraying pressure of 0.8-1.2MPa, forming a wet film thickness of 150-200μm. The conversion relationship between wet film thickness and dry film thickness satisfies... , where d 干 d represents the dry film thickness (μm). 湿 is the wet film thickness (μm), w is the percentage of volatile matter in the coating material (%), and w is controlled to be ≤15% to ensure the dry film thickness accuracy is ±10μm.

[0044] (iv) Curing treatment:

[0045] The coated gate valve is placed in a constant temperature chamber. The curing process is controlled by a PLC program to control the heating rate. Initially, the temperature is increased by 5-8℃ / min. When the temperature reaches 80℃, the heating rate is automatically adjusted to 3-5℃ / min. After reaching 120-150℃, the temperature is maintained for 2-3 hours. Then, the valve is cooled to room temperature in the furnace to avoid stress cracks inside the coating.

[0046] (v) Inspection and Acceptance:

[0047] The coating thickness is measured using an eddy current thickness gauge, requiring an average thickness ≥200μm. The coating adhesion is tested using a cross-cut adhesion test with a 1mm spacing, achieving a rating of Class 0 in ISO 2409. The coating surface pencil hardness is measured, requiring ≥2H. Furthermore, the coating must pass a 5% NaCl solution salt spray test for ≥1000 hours without rust. Additionally, plasma treatment can be applied to the coating surface, using an Ar atmosphere (pressure 10-30Pa) at 30-50W power for 5-10 minutes to further improve the coating surface density.

[0048] Example 1:

[0049] Pretreatment: 100-mesh quartz sand was selected, the blasting pressure was set to 0.5 MPa, the blasting pipe diameter was 8 mm, the sand density was 2.65 g / cm³, and the sand particle size was 0.3 mm. The sand particle velocity was calculated according to the formula. The velocity is approximately 0.61 m / s, which is converted to 36.6 m / s. Under this parameter, the outer surface of the gate valve is sandblasted until the surface roughness Ra reaches 9 μm. Before sandblasting, the gate valve is immersed in an 8% NaOH solution at 70°C and cleaned with ultrasonic waves at a frequency of 50 kHz for 12 minutes.

[0050] Coating preparation: Take 10 kg of epoxy resin, add 2.5 kg of curing agent at a mass ratio of 1:4, and add the mass of nano-Al2O3 particles. =0.56kg, and at the same time add 0.3kg of graphene nanosheets, and stir evenly to obtain the coating material.

[0051] Spray coating application: Under ambient temperature of 22℃ and humidity of 55%, use a high-pressure airless sprayer with a nozzle orifice diameter of 1mm, a spraying distance of 180mm, and a spraying pressure of 1MPa to form a wet film thickness of 180μm. Control the volatile content of the coating material to 12%. The calculated dry film thickness... .

[0052] Curing treatment: Place the sprayed gate valve into a constant temperature chamber and heat it at 6℃ / min. After reaching 80℃, adjust the temperature to 4℃ / min and heat it to 130℃. Hold the temperature for 2.5 hours and then cool it with the furnace.

[0053] Inspection and acceptance: The average coating thickness was 210μm as measured by an eddy current thickness gauge; the adhesion test by cross-cut test reached level 0; the pencil hardness was 3H; no rust was observed after 1200h of salt spray test with 5% NaCl solution; finally, plasma treatment was carried out for 8min under Ar gas pressure of 20Pa and power of 40W.

[0054] Example 2:

[0055] Pretreatment: Quartz sand with a particle size of 80 mesh, sandblasting pressure of 0.4 MPa, and a calculated sand particle velocity of 30 m / s, resulting in a surface roughness Ra of 6.3 μm after treatment. The gate valve was ultrasonically cleaned for 10 min at 40 kHz in a 5% NaOH solution at 60℃.

[0056] Coating preparation: 8 kg epoxy resin, 2 kg curing agent, and the amount of nano-Al2O3 particles added:

[0057] =0.45kg, graphene nanosheets 0.2kg.

[0058] Spraying application: Temperature 20℃, humidity 60%, nozzle orifice diameter 0.8mm, spraying distance 150mm, pressure 0.8MPa, wet film thickness 150μm, dry film thickness 132μm (volatile matter 12%).

[0059] Curing process: Increase the temperature to 80℃ at 5℃ / min, then increase it to 120℃ at 3℃ / min, and hold for 3 hours.

[0060] Inspection and acceptance: The average coating thickness is 205μm, the adhesion is grade 0, the pencil hardness is 2H, and there is no rust after 1100h of salt spray test. The plasma treatment conditions are Ar gas pressure 10Pa, power 30W, and time 5min.

[0061] Example 3:

[0062] Pretreatment: Quartz sand particle size 120 mesh, sandblasting pressure 0.6 MPa, sand particle velocity 50 m / s, surface roughness Ra reaches 12.5 μm. Gate valve is ultrasonically cleaned for 15 min at 60 kHz in 10% NaOH solution at 80℃.

[0063] Coating preparation: 12 kg epoxy resin, 3 kg curing agent, and m= nano Al2O3 particles =0.75kg, graphene nanosheets 0.4kg.

[0064] Spraying application: Temperature 25℃, humidity 50%, nozzle orifice diameter 1.2mm, spraying distance 200mm, pressure 1.2MPa, wet film thickness 200μm, dry film thickness 170μm (volatile matter 15%).

[0065] Curing process: Heat to 80℃ at 8℃ / min, then heat to 150℃ at 5℃ / min and hold for 2 hours.

[0066] Inspection and acceptance: The average coating thickness is 220μm, the adhesion is grade 0, the pencil hardness is 3H, there is no rust after 1300h of salt spray test, and the plasma treatment is carried out for 10min under Ar gas pressure of 30Pa and power of 50W.

[0067] Comparative Example 1:

[0068] Using traditional processes, the pretreatment only involves sanding the gate valve surface; the coating preparation uses a 3:1 mixture of ordinary epoxy resin and curing agent, without adding nanoparticles or graphene nanosheets; the spraying is done by air spraying, resulting in unstable control of the wet film thickness; curing is done by natural drying at room temperature; and rigorous testing such as salt spray testing is not performed.

[0069] Comparative Example 2:

[0070] The pretreatment was the same as in Example 1, but only 5% of nano-Al2O3 particles were added to the coating preparation, and no graphene nanosheets were added; the spraying and curing process parameters were basically the same as in Example 1, but the relevant parameters were not precisely controlled by formula; the inspection and acceptance were only carried out by testing the coating thickness and adhesion.

[0071] Comparative Example 3:

[0072] The pretreatment, coating preparation and spraying processes were the same as in Example 1, but the curing process used a constant heating rate of 8℃ / min, directly heating to 150℃ and holding for 2h; no plasma post-treatment was performed; and no pencil hardness test was performed during inspection and acceptance.

[0073] Data comparison and analysis:

[0074]

[0075] The data comparison shows that:

[0076] Comparison of Example 1 and Comparative Example 2: This invention, through sandblasting pretreatment, nanoparticle-reinforced coating, and precise spray curing process, significantly outperforms traditional processes in terms of coating thickness, adhesion, pencil hardness, and salt spray test time. Traditional processes, lacking effective surface treatment and high-performance coating materials, result in poor coating performance and insufficient corrosion resistance.

[0077] Comparison of Example 1 with Comparative Example 2: Although Comparative Example 2 added nano-Al2O3 particles, it did not add graphene nanosheets, and some process parameters were not precisely controlled, resulting in lower salt spray test time and dry film thickness accuracy than Example 2. This shows that the addition of graphene nanosheets and precise parameter control play an important role in improving coating performance.

[0078] Comparison of Example 3 with Comparative Example 4: Comparative Example 3 did not use segmented temperature control during the curing process and did not perform plasma post-treatment, which may have caused stress inside the coating, affecting the salt spray test performance and pencil hardness. This shows that the curing process and post-treatment steps are crucial to the final coating quality.

[0079] In summary, this invention effectively improves the overall performance of the outer surface coating of the gate valve through optimized design of each process step, addition of specific materials, and precise parameter control, and has significant advantages compared with traditional processes and some improved processes.

[0080] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A gate valve external surface treatment process, characterized in that: Includes the following steps: S1： Pretreatment: The outer surface of the gate valve is sandblasted with quartz sand of 80-120 mesh at a pressure of 0.4-0.6 MPa until the surface roughness Ra reaches 6.3-12.5 μm; S2: Coating preparation: Mix epoxy resin and curing agent at a mass ratio of (3-5):1, add 5-8% of nano Al2O3 particles, stir evenly to obtain coating material; S3: Spraying construction: Using high-pressure airless spraying equipment, under the conditions of temperature 20-25℃ and humidity ≤60%, the coating material is sprayed onto the surface of the gate valve at a spraying pressure of 0.8-1.2MPa to form a wet film thickness of 150-200μm. S4: Curing treatment: Place the sprayed gate valve in a constant temperature chamber and raise the temperature to 120-150℃ at a rate of 5-8℃ / min. Keep it at this temperature for 2-3 hours and then cool it to room temperature with the furnace. S5: Inspection and Acceptance: The coating thickness is tested using an eddy current thickness gauge. The average thickness is required to be ≥200μm, and the coating must pass a 5% NaCl solution salt spray test for ≥1000h without rust.

2. The gate valve external surface treatment process as described in claim 1, characterized in that, The velocity of the sand particles in the sandblasting process in step S1 is calculated using the following formula: ； Where P is the sandblasting pressure, ρ is the sand particle density, d is the sand particle size, and D is the diameter of the sandblasting pipe, the sand particle velocity is controlled within the range of 30-50m / s.

3. The gate valve outer surface treatment process as described in claim 2, characterized in that, The amount of nano-Al2O3 particles added in step S2 is determined by the following formula: ； Where m is the mass of nanoparticles, m0 is the mass of epoxy resin, and Ra is the surface roughness after pretreatment, ensuring that the bonding strength between the coating and the substrate is ≥50MPa.

4. The gate valve outer surface treatment process as described in claim 3, characterized in that, The conversion relationship between the wet film thickness and the dry film thickness in step S3 of the spraying process satisfies: , where d 干 d represents the dry film thickness. 湿 denoted as wet film thickness, and w as the percentage of volatile components in the coating material. w is controlled to be ≤15% to ensure a dry film thickness accuracy of ±10μm.

5. The gate valve outer surface treatment process as described in claim 4, characterized in that, The heating rate of the curing process in step S4 is controlled by a PLC program. When the temperature reaches 80℃, the heating rate is automatically adjusted to 3-5℃ / min to avoid stress cracks in the coating.

6. The gate valve outer surface treatment process as described in claim 5, characterized in that, Before the sandblasting treatment in step S1, the gate valve is first immersed in a 5-10% NaOH solution at 60-80℃ and ultrasonically cleaned for 10-15 minutes to remove surface oil. The ultrasonic frequency is controlled at 40-60kHz.

7. The gate valve outer surface treatment process as described in claim 6, characterized in that, In step S2, the coating material also includes 2-4% graphene nanosheets to improve the coating's corrosion resistance and extend the salt spray test time by more than 20%.

8. The gate valve outer surface treatment process as described in claim 7, characterized in that, During the inspection and acceptance process in step S5, the coating adhesion is tested using the cross-cut test with a cross-cut spacing of 1 mm. The coating achieves a rating of level 0 in the ISO2409 standard, and the pencil hardness of the coating surface is ≥2H.

9. The gate valve outer surface treatment process as described in claim 8, characterized in that, The nozzle diameter of the spraying equipment in step S3 is 0.8-1.2mm, and the spraying distance is controlled at 150-200mm to ensure that the coating surface uniformity error is ≤5%.

10. The gate valve outer surface treatment process as described in claim 9, characterized in that, It also includes a post-processing step: the outer surface of the cured gate valve is treated with plasma treatment equipment in an Ar atmosphere at a power of 30-50W for 5-10 minutes to further improve the density of the coating surface.

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