Full-automatic galvanizing method for steel pipe

Abstract

The invention provides a full-automatic steel pipe galvanizing method, which relates to the technical field of steel pipe surface treatment, and is technically characterized by comprising the following steps: feeding by a full-automatic mechanical arm, conveying to a detection station by a roller way, and screening steel pipes with qualified appearances and sizes by machine vision and laser length measurement; the qualified steel pipe is sequentially subjected to degreasing treatment, acid pickling activation, neutralization passivation and low-temperature stress elimination; rough polishing is conducted after pretreatment, fine polishing is conducted after zinc ammonium chloride assistant plating, and the surface state matched with zinc layer deposition is formed; the steel pipe subjected to secondary grinding is vertically immersed into a zinc pot for galvanization, zinc serves as a base body of a galvanization solution, and aluminum and rare earth elements are added; the steel pipe is sequentially subjected to primary blowing, 3D visual identification and self-adaptive blowing after being galvanized; and cooling and discharging. According to the full-automatic galvanizing method for the steel pipe, the whole process is automatically controlled, manual intervention is not needed from raw material feeding to finished product discharging, the production efficiency is improved, and meanwhile quality fluctuation caused by manual operation is avoided.

Description

Technical Field

[0001] This invention relates to the field of steel pipe surface treatment technology, and in particular to a fully automatic galvanizing method for steel pipes. Background Technology

[0002] Steel pipes, as a basic industrial material, are widely used in construction, petroleum, chemical, and water conservancy fields. Their corrosion resistance directly affects their service life and safety. Galvanizing is the core process for improving the corrosion resistance of steel pipes. However, traditional galvanizing methods often suffer from problems such as low automation, crude control of process parameters, uneven coating quality, and excessive manual intervention.

[0003] For example, the material feeding process relies on manual screening for appearance defects, leading to unqualified products flowing into subsequent processes; during the galvanizing process, parameters such as temperature and time fluctuate greatly, which can easily cause problems such as coating peeling and uneven thickness; the air blowing process cannot be adaptively adjusted according to the actual size of the steel pipe, and residual zinc in the inner layer can easily cause blockage.

[0004] Crucially, traditional grinding processes often employ a "single-pass rough grinding" or "pre-treatment grinding only" approach, making it difficult to balance the conflict between the "cleanliness" of the steel pipe surface and the "coating adhesion." Over-grinding can lead to a smooth surface, reducing coating adhesion, while under-grinding leaves residual impurities, causing coating defects and becoming a significant bottleneck restricting galvanizing quality. Therefore, developing a fully automated steel pipe galvanizing method with precise and controllable process parameters and innovative grinding technology is of great significance for improving product quality and production efficiency. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that traditional grinding processes in the prior art are unable to balance the contradiction between the "cleanliness" and "coating adhesion" of the steel pipe surface.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A fully automated galvanizing method for steel pipes, characterized by comprising the following steps: S1: The fully automatic feeding robot arm clamps the steel pipes for feeding, and the pipes are transported by roller conveyor. During the transport process, the surface defects and dimensional deviations of the steel pipes are detected, and steel pipes that meet the appearance and size requirements are selected. S2: The qualified steel pipes are sequentially subjected to degreasing, pickling and activation, neutralization and passivation and low-temperature stress relief. The low-temperature stress relief is carried out under nitrogen protection, with an annealing temperature of 200-250℃ and a holding time of 10-15 minutes. S3: The pretreated steel pipe is first roughly ground, then treated with zinc chloride ammonium solvent for fluxing, and then finely ground to form a surface state suitable for zinc layer deposition. S4: The steel pipe after secondary grinding is vertically immersed into the zinc pot for galvanizing. The temperature of the zinc pot is controlled at 450-480℃. The galvanizing solution uses zinc as the base and adds aluminum and rare earth elements. S5: After galvanizing, the steel pipe undergoes primary air blowing, 3D vision recognition, and adaptive air blowing in sequence. The air blowing parameters are adjusted according to the distribution of zinc liquid on the surface of the steel pipe to control the coating thickness. S6: The steel pipe is cooled by a combination of spraying and immersion. Then, the coating quality is detected by 3D visual scanning and ultrasonic thickness measurement. Qualified finished products are unloaded by a fully automatic robotic arm and production parameters are recorded to achieve quality traceability.

[0007] Preferably, the degreasing treatment in S2 uses an alkaline solution with the following proportions: sodium hydroxide 8-12 g / L, sodium carbonate 15-20 g / L, trisodium phosphate 5-8 g / L, surfactant 2-3 g / L; degreasing temperature 50-60℃; spray pressure 0.3-0.5 MPa; and treatment time 3-5 minutes. Pickling activation uses a 15-20 wt% hydrochloric acid solution at a temperature of 20-30℃ for 2-4 minutes. During the pickling process, compressed air bubbles with a diameter of 0.5-1 mm are introduced for stirring. Neutralization and passivation use a 10-15 wt% sodium carbonate solution for 1-2 minutes to ensure that the pH value of the steel pipe surface is stable at 7-8.

[0008] Preferably, in the S3 coarse grinding, a 300-400 mesh alumina abrasive belt is used, the grinding speed is 300-500 rpm, the grinding head pressure is 0.2-0.8 MPa, and 2-4 grinding heads are set according to the diameter of the steel pipe; Fine grinding uses 500-600 grit silicon carbide abrasive belts, with a grinding speed of 400-600 rpm, and the grinding time is shortened by 20-30% compared to coarse grinding.

[0009] Preferably, a negative pressure dust collection device is used to collect dust during the rough grinding and fine grinding processes, with a dust collection wind speed of 15-20 m / s.

[0010] Preferably, in the zinc chloride ammonium solvent fluxing treatment in S3, the solvent ratio is 15-20 wt% zinc chloride, 25-30 wt% ammonium chloride, and 0.5-1 wt% stannous chloride; the solvent temperature is 60-80℃; the steel pipe immersion speed is 0.3-0.5 m / min; the immersion time is 3-5 minutes; and after immersion, the excess solvent is removed by natural dripping for 1-2 minutes.

[0011] Preferably, the mass percentages of the zinc liquid components in S4 are as follows: zinc 95-97%, aluminum 2-4%, rare earth elements 0.1-0.3%, wherein the rare earth elements are a mixture of cerium and lanthanum, and a stirring device is provided at the bottom of the zinc pot with a stirring speed of 50-80 rpm.

[0012] Preferably, the specific steps of S5 are as follows: The primary air blowing uses an inner and outer double-layer air blowing ring, with an outer layer wind speed of 8-12m / s and an air blowing time of 2-3 seconds; The 3D visual recognition system uses a binocular 3D camera with a measurement accuracy of ±0.01 mm and a recognition time of ≤0.5 seconds. The adaptive blowing outer layer has a wind speed of 6-10 m / s, the inner layer has a wind speed of 10-15 m / s, and the radial adjustment range of the blowing ring is ±5 mm, ensuring that the coating thickness deviation is ≤5 μm.

[0013] Preferably, in step S6, the spray cooling water temperature is 15-25℃, the pressure is 0.2-0.4 MPa, and the spraying time is 3-5 minutes; the immersion cooling water temperature is 20-30℃, the immersion time is 5-7 minutes, and the temperature of the steel pipe after cooling is ≤60℃.

[0014] Preferably, in S1, the gripping force of the robotic arm is 50-80 N, the roller conveyor speed is 1-2 m / min, the machine vision uses 3 sets of 12-megapixel industrial cameras, the shooting frequency is 10-15 frames / second, the laser length measurement accuracy is ±0.5 mm, and the length tolerance is controlled within ±2 mm.

[0015] This application also provides a galvanized steel pipe, which is prepared using the method described in any one of claims 1-9.

[0016] Compared with the prior art, this application has the following beneficial effects: 1. The fully automatic galvanizing method for steel pipes provided in this application has fully automated control of the entire process. No manual intervention is required from raw material feeding to finished product unloading, which increases production efficiency by more than 40%. At the same time, it avoids quality fluctuations caused by manual operation, and increases the product qualification rate from 85% in the traditional method to more than 98%.

[0017] 2. The parameters such as temperature, time, and speed in each stage of this application are precisely controlled by a central control system. For example, the galvanizing temperature fluctuation is ≤±2℃ and the coating thickness deviation is ≤5μm, ensuring consistent product quality.

[0018] 3. The coating adhesion is improved by adding pretreatment and stress relief processes. Combined with double polishing and adaptive air blowing technology, the coating's salt spray corrosion resistance time reaches more than 1,000 hours, far exceeding that of traditional zinc-plated products (around 600 hours).

[0019] 4. By adopting technologies such as negative pressure dust collection and nitrogen protection, dust and harmful gas emissions are reduced; rare earth elements are added to the zinc liquid to improve zinc utilization and reduce zinc consumption by 10-15%, which meets the requirements of green production. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating a fully automated galvanizing method for steel pipes according to one embodiment of this application. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments.

[0022] Please see Figure 1 This application provides a fully automatic galvanizing method for steel pipes, which includes the following steps: S1: Material loading and appearance inspection: The steel pipes are placed from the stacked state onto the roller conveyor by a fully automatic feeding robot arm. The clamping force of the robot arm is controlled at 50-80N, and the roller conveyor speed is set to 1-2m / min.

[0023] In one embodiment, the speed of the roller conveyor can be adaptively adjusted according to the diameter of the steel pipe.

[0024] During the roller conveyor process, the appearance of the steel pipe is inspected using machine vision and laser length measurement. Specifically, in one embodiment, the surface of the steel pipe is inspected using three sets of high-definition industrial cameras and two sets of side light sources. The high-definition industrial cameras have a resolution of 12 megapixels and a shooting frequency of 10-15 frames per second. The high-definition industrial cameras acquire images from the top, bottom, and sides of the steel pipe, and the algorithm identifies defects such as surface cracks, dents, scratches (those with a depth ≥ 0.2 mm or a length ≥ 5 mm are considered unqualified), and corrosion. The steel pipe length is measured using a laser length sensor with a measurement accuracy of ±0.5mm and a measurement range of 0.5-12m. If the measured length does not conform to the preset tolerance (±2mm), it is deemed unqualified. Unqualified steel pipes are automatically moved to the unqualified product bin by a rejection robotic arm, while qualified steel pipes enter the pre-processing stage.

[0025] The automated and non-destructive introduction of steel pipes is achieved through robotic arms and roller conveyor devices, while non-conforming products with inconsistent appearance and dimensions are screened out at the front end of the process to avoid subsequent ineffective processing.

[0026] In addition, the use of robotic arms for gripping can effectively prevent the steel pipe surface from being damaged.

[0027] S2: Pre-treatment of steel pipes: First, the appearance of the steel pipes is inspected, and the steel pipes that pass the appearance inspection are degreased. After the degreasing treatment is completed, they are immediately sent to pickling and activation. After pickling, the steel pipes are sent to a neutralization tank for neutralization and passivation. After neutralization and passivation, the steel pipes are sent to a continuous low-temperature annealing furnace for stress relief treatment.

[0028] In one embodiment, the specific steps of the pretreatment of the steel pipe are as follows: S21: The steel pipes that pass the appearance inspection are sent into a closed degreasing tank and degreased by spraying with an alkaline degreasing solution.

[0029] The degreasing solution is prepared with the following proportions: sodium hydroxide 8-12 g / L, sodium carbonate 15-20 g / L, trisodium phosphate 5-8 g / L, surfactant 2-3 g / L, and the remainder deionized water. The degreasing temperature is controlled at 50-60℃, the spray pressure is 0.3-0.5 MPa, and the treatment time is 3-5 minutes. During the degreasing process, the steel pipe is sprayed 360° without dead angles through a rotating conveyor mechanism, ensuring that surface oil and impurities are thoroughly removed. The degreasing tank is used to directionally remove organic impurities such as oil, cutting fluid residue, and dust adhering to the surface of the steel pipe during rolling and storage, preventing these impurities from forming a "separation layer" in subsequent pickling and coating processes.

[0030] S22: After degreasing, the steel pipe is immediately sent to the pickling tank and pickled with hydrochloric acid solution to dissolve the oxide scale, rust and rolling oxidation products on the surface of the steel pipe. At the same time, the base surface is slightly etched to form an activated metal surface.

[0031] The hydrochloric acid concentration should be controlled at 15-20 wt%, the solution temperature at 20-30℃, and the pickling time at 2-4 minutes. During the pickling process, compressed air is continuously introduced through a bubble agitator, with the bubble diameter controlled at 0.5-1mm and the agitation frequency at 5-8 times / second, to prevent excessive corrosion on the steel pipe surface.

[0032] S23: After pickling, the steel pipe is sent to a neutralization tank for neutralization and passivation, which terminates the corrosive effect of residual acid, neutralizes acidic substances on the surface, and prevents the steel pipe from being oxidized again in the air after pickling.

[0033] The neutralization tank contains a 10-15 wt% sodium carbonate solution at room temperature for 1-2 minutes to ensure complete neutralization of residual acid on the steel pipe surface and stabilize the pH value at 7-8.

[0034] S24: After neutralization, the steel pipe is sent to a continuous low-temperature annealing furnace for stress relief treatment. The annealing temperature is controlled at 200-250℃, the heating rate is 5-8℃ / min, the holding time is 10-15 minutes, the cooling rate is 3-5℃ / min, and the furnace exit temperature is ≤50℃.

[0035] Nitrogen protection is used during the annealing process. The nitrogen purity is ≥99.9%, and the protective gas flow rate is 1-2 m³ / h. 3 / h, to prevent oxidation of the steel pipe surface. After stress relief is completed, the steel pipes are stacked and placed in preparation for the next process.

[0036] Degreasing and pickling remove impurities, scale, and rust from the steel pipe surface, providing a clean and activated substrate for subsequent coating adhesion and improving coating bonding strength. Furthermore, low-temperature stress relief releases internal stress generated during steel pipe rolling, preventing coating cracking or peeling after galvanizing due to stress release. This operation effectively reduces the scrap rate. Nitrogen protection prevents secondary oxidation of the steel pipe, reducing subsequent grinding work and thus effectively improving production efficiency.

[0037] S3: Zinc chloride ammonium solvent coating The pre-treated steel pipe is then polished using an alumina abrasive belt (300-400 grit) at a speed of 300-500 rpm. The polishing length is the full length of the steel pipe, and the polishing time is calculated based on the pipe length (e.g., 2-3 minutes for a 6m long pipe). The number of polishing heads is determined by the pipe diameter (2 heads for φ10-φ50mm, 4 heads for φ50-φ200mm), and the polishing head pressure is adaptively adjusted (range 0.2-0.8MPa).

[0038] Grinding removes the tiny oxide scale, rolling burrs, and pinpoint rust residue remaining on the surface of the steel pipe after pretreatment, while simultaneously creating a macroscopically rough surface suitable for plating.

[0039] After grinding, the steel pipe is sent into a solvent bath for assisted plating. The solvent bath is equipped with a constant temperature heating device, and the temperature is controlled at 60-80℃ with a temperature fluctuation range of ±1℃.

[0040] The zinc chloride ammonium solvent ratio is: zinc chloride 15-20wt%, ammonium chloride 25-30wt%, stannous chloride 0.5-1wt%, and the balance is deionized water. The solution pH is controlled at 5.5-6.5. The solution concentration is checked every 8 hours. When the zinc chloride content is lower than 15wt% or the ammonium chloride content is lower than 25wt%, it is automatically replenished.

[0041] The steel pipe is immersed in the solvent vertically and slowly at a speed of 0.3-0.5 m / min to ensure uniform solvent adhesion to the surface of the pipe. The total immersion time is 3-5 minutes, adjusted according to the pipe diameter; for every 20 mm increase in diameter, the immersion time increases by 0.5 minutes. After immersion, the steel pipe is slowly removed from the solvent bath at a speed of 0.2-0.3 m / min and allowed to drip naturally for 1-2 minutes to remove excess solvent from the surface.

[0042] A uniform zinc chloride film is formed on the surface of the steel pipe by using zinc chloride ammonium solvent. This film serves as a "transitional bonding layer" between the zinc liquid and the substrate, inhibiting the high-temperature oxidation of the substrate during the galvanizing process and enhancing the deposition activity of zinc atoms.

[0043] S4: Fully automatic galvanizing: After the ammonium chloride solvent coating is completed, the steel pipe is ground with a 500-600 mesh silicon carbide abrasive belt at a grinding speed of 400-600 rpm. The grinding length is the same as the full length of the steel pipe, and the grinding time is reduced by 20-30% compared to the previous grinding (for example, the grinding time for a 6m long steel pipe is 1.5-2 minutes). The grinding head parameters are the same as those for rough grinding to ensure uniform grinding.

[0044] This polishing is mainly used to refine the surface of the steel pipe, remove the tiny particles generated during the solvent plating process, improve the surface roughness to Ra0.8-1.6μm, and enhance the adhesion of the subsequent zinc layer.

[0045] During the polishing process, a negative pressure dust collection device is used to collect dust, with a dust collection speed of 15-20m / s, to ensure a clean working environment and prevent dust from adhering and affecting the coating quality.

[0046] The above polishing process removes crystalline protrusions and microparticles formed during solvent plating, refines the surface roughness to a range suitable for zinc layer deposition, and slightly activates the solvent film surface to enhance reactivity. A second polishing process refines the steel pipe surface roughness to Ra0.8-1.6μm, improving surface smoothness by 60%.

[0047] Through a tiered design of "coarse grinding for impurities + fine grinding for roughening," the conflict between "cleanliness" and "adhesion" is balanced, providing the optimal surface condition for subsequent galvanizing; dust control avoids secondary pollution. Compared with traditional single grinding, the coating thickness uniformity is improved by 60%, and the adhesion qualification rate is improved by 43 percentage points; the dust collection device ensures that the dust concentration in the working environment is ≤0.5mg / m³, which meets the GBZ2.1-2019 occupational health standard, while the coating defect rate caused by dust adhesion is reduced to below 0.3%.

[0048] After grinding, the steel pipes are sent into a fully automatic zinc pot for galvanizing. The zinc pot uses induction heating, and the temperature is controlled at 450-480℃ with a temperature fluctuation of ≤±2℃.

[0049] In one embodiment, the zinc liquid composition in the fully automatic zinc pot is: 95-97 wt% zinc, 2-4 wt% aluminum, and 0.1-0.3 wt% rare earth elements (cerium, lanthanum).

[0050] The addition of aluminum enhances the corrosion resistance of the zinc coating, while rare earth elements refine the zinc grains and improve the uniformity of the coating structure.

[0051] The steel pipe is vertically immersed into the zinc pot at a speed of 0.4-0.6 m / min to ensure stable adhesion of the zinc liquid. The galvanizing time is adjusted according to the diameter of the steel pipe and the required coating thickness. When a coating thickness of 60-80 μm is required, the galvanizing time for φ10-φ50 mm steel pipes is 1-1.5 minutes, and for φ50-φ200 mm steel pipes, it is 1.5-2.5 minutes. During the galvanizing process, a stirring device is installed at the bottom of the zinc pot at a stirring speed of 50-80 rpm to prevent the zinc liquid from separating. After galvanizing, the steel pipe is slowly removed from the zinc pot at a speed of 0.3-0.4 m / min, protected by a nitrogen gas curtain during the removal process to prevent oxidation of the zinc layer.

[0052] In this application, the mechanical properties and corrosion resistance of the zinc coating are improved by adding alloying elements and controlling the process. Furthermore, the oxidation rate of the zinc coating surface is ≤2% by using a nitrogen gas curtain, avoiding the "gray zinc" defect in the traditional process, and the surface gloss of the coating is improved by 40%.

[0053] S5: Segmented blowing In one embodiment, the air blowing process is divided into two stages: "primary air blowing" and "adaptive air blowing". High-pressure air is used as the blowing medium. The air is dried and degreased (moisture content ≤0.01g / m³, oil content ≤0.001mg / m³) to ensure that the zinc layer is not contaminated.

[0054] The specific steps are as follows: S51: After the steel pipe is removed from the galvanizing pot, it immediately enters the primary air blowing station. This station is equipped with inner and outer double-layer air blowing rings. The outer air blowing ring has 8-12 nozzles (1-2mm in diameter), and the inner air blowing ring has 4-6 nozzles (0.5-1mm in diameter). The primary air blowing velocity is controlled at 8-12m / s, and the blowing time is 2-3 seconds. Its main function is to quickly remove a large amount of excess zinc liquid from the surface of the steel pipe and initially control the coating thickness.

[0055] Primary air blowing is to quickly remove excess zinc liquid from the surface before the zinc liquid completely solidifies, thus avoiding the "slag" defect caused by the natural dripping of zinc liquid.

[0056] S52: After the initial air blowing, the steel pipe enters the 3D vision recognition area. The binocular 3D camera (measurement accuracy ±0.01mm) quickly collects the surface contour data of the steel pipe, identifies the diameter, roundness and zinc liquid distribution on the surface of the steel pipe, and transmits the data to the central control system to provide parameter basis for adaptive air blowing. The recognition time is ≤0.5 seconds.

[0057] S53: Based on 3D visual recognition data, the central control system automatically adjusts the blowing parameters. The outer layer blowing speed can adaptively vary within the range of 6-10m / s, increasing the speed in areas with accumulated zinc and decreasing it in areas with thinner zinc layers. The inner layer blowing speed is controlled at 10-15m / s, and the position of the blowing ring is adjusted according to changes in the inner diameter of the steel pipe (radial adjustment range ±5mm) to ensure that excess zinc on the inner wall is thoroughly removed. The adaptive blowing time is 3-5 minutes to ensure uniform outer coating thickness (deviation ≤5μm), no zinc residue on the inner layer, and a smooth inner wall.

[0058] In this application, segmented air blowing is used to control the thickness of the inner and outer coatings, eliminate local accumulation and residue, and ensure the dimensional accuracy and surface quality of the coatings.

[0059] S6: Galvanized steel pipe cooling After the air blowing is completed, the steel pipe is sent into a water cooling device for cooling, using a combination of "spraying + immersion" cooling method.

[0060] Specifically, in one embodiment, the steel pipe is first cooled by high-pressure spraying, with the cooling water temperature controlled at 15-25℃, the spraying pressure at 0.2-0.4MPa, and the spraying time at 3-5 minutes. Subsequently, it is immersed in a cooling water tank at 20-30℃ for 5-7 minutes, for a total cooling time of 8-12 minutes. After cooling, the steel pipe temperature is controlled at 40-60℃ to avoid excessively high temperatures that could lead to errors in subsequent testing or burns to personnel.

[0061] After cooling, the steel pipe undergoes 3D visual inspection using structured light scanning and image analysis. In one embodiment, the inspection device consists of two structured light scanners and an image analysis system. The structured light scanners have a scanning accuracy of 0.02 mm. The structured light scanners and the image analysis system are used to scan the inner and outer surfaces of the steel pipe, respectively. The outer surface inspection focuses on the distribution of the coating and surface defects. In one embodiment, the coating thickness distribution is assisted by an ultrasonic thickness measurement module. The surface defects include bulges and pinholes.

[0062] The key points of the inner surface inspection are the smoothness of the inner wall, the presence of zinc nodules and blockage. In one embodiment, the roughness of the inner surface is set to be ≤ Ra1.6μm to be qualified.

[0063] Simultaneously, the scanned data generates a 3D model of the steel pipe, providing precise positioning coordinates for the robotic gripper (positioning accuracy ±0.1mm), ensuring a smooth unloading process. Products that fail inspection are automatically marked and sent to the rework station, while qualified products proceed to the unloading stage.

[0064] S7: Unloading Based on positioning data provided by 3D vision inspection, a fully automated unloading robotic arm precisely clamps both ends of the steel pipe (clamping force 40-70N to avoid damaging the coating), transferring the steel pipe from the conveyor rollers to the finished product rack. The finished product rack adopts a layered design, with buffer pads on each layer, and the steel pipes are placed at intervals of ≥50mm to avoid collisions. After unloading, the central control system records the production parameters of this batch of steel pipes (such as galvanizing time, temperature, coating thickness, etc.), enabling product quality traceability.

[0065] The above content will be explained in conjunction with specific verification experiments: I. Experimental Materials and Equipment: 1. Experimental Samples Four typical steel pipe specifications (φ20mm×2m, φ50mm×3m, φ100mm×4m, φ150mm×6m) were selected, and two sets of samples were prepared for each specification. Group A was galvanized using the fully automatic galvanizing method of this invention, and Group B was galvanized using the traditional manual galvanizing method (without pretreatment stress relief and fixed parameter air blowing). The number of samples in each group was 10 to ensure that the samples were statistically representative.

[0066] 2. Experimental equipment Coating thickness test: Eddy current thickness gauge (accuracy ±0.1μm, model: Fischer FMP100), conforming to GB / T4956-2003 "Magnetic method for measuring the thickness of non-magnetic coating on magnetic substrate" standard; (2) Salt spray corrosion test: Neutral salt spray test chamber (model: LYW-015, volume 150L, ​​temperature control accuracy ±1℃, spray volume 1-2mL / (h·80cm²)), conforming to GB / T 10125-2021 "Salt spray test for corrosion test in artificial atmosphere" standard; (3) Auxiliary equipment: Micrometer (accuracy 0.01mm), electronic balance (accuracy 0.001g), surface roughness tester (model: TR200, accuracy ±0.01μm), constant temperature drying oven (temperature range 0-200℃).

[0067] II. Experimental Procedure:

[0068] (1) Sampling and marking: Randomly select 3 steel pipes from each specification of the two groups A and B, and select 5 test sections on each steel pipe, namely the two ends of the steel pipe (50mm away from the port) and the middle area (3 sections evenly distributed). Select 4 test points evenly along the circumference of each section and mark the test position with a marker to avoid repetition or omission.

[0069] (2) Thickness measurement: After calibrating the eddy current thickness gauge (zero point calibration is performed using a standard calibration piece), each detection point is measured sequentially. Each point is measured 3 times consecutively, the data is recorded and outliers (data that deviate from the average value by ±5%) are removed. The average value of the remaining 2 data is taken as the coating thickness value of that point.

[0070] (3) Data statistics: Calculate the average coating thickness and maximum thickness deviation (the maximum difference between the thickness of each test point on a single steel pipe and the average value) of each steel pipe, and statistically analyze the mean and standard deviation of the thickness deviation of the same specification sample group to evaluate the thickness uniformity.

[0071] 2. Salt spray corrosion resistance test (1) Sample pretreatment: Wipe the surface of the remaining 7 samples of each specification in groups A and B with anhydrous ethanol to remove oil and impurities, place them in a constant temperature drying oven (60℃) and dry for 30 minutes. After cooling to room temperature, weigh them (recorded as ). ).

[0072] (2) Salt spray test parameter settings: The test type is neutral salt spray (NSS), the salt concentration is 50±5g / L (sodium chloride purity ≥99.5%, prepared with deionized water), the solution pH value is 6.5-7.2, the test temperature is 35±1℃, the spray pressure is 0.7-1.0bar, and the spray is continuous.

[0073] (3) Test procedure and observation: Place the sample in the salt spray test chamber at an angle of 15-30° to the vertical direction to ensure that the salt spray evenly covers the surface. Take out the sample at 24h, 48h, 72h, 100h, 200h, 500h, 800h and 1000h respectively, rinse the surface salt with running deionized water (water temperature 25±5℃, rinsing time 30s), and observe the surface corrosion after drying (whether red rust and white rust appear and the corrosion area), and record the time when red rust first appears (i.e. corrosion failure time).

[0074] (4) Corrosion rate calculation: After the test (when red rust appears on the sample or 1000h is reached), remove the corrosion products from the sample surface, dry it, and weigh it (recorded as m1). Calculate the corrosion rate according to the formula: , where S is the sample surface area (m²) and t is the test time (h).

[0075] 3. Auxiliary verification experiment on coating adhesion The cross-cut test was used to verify the adhesion of the coating (refer to GB / T 9286-1998). A 10×10 grid with a spacing of 1 mm was cut on the surface of the samples in groups A and B with a cross-cut knife, down to the steel pipe substrate. The grid was then quickly peeled off with tape, and the coating peeling off within the grid was observed and rated from 1 to 5 (1 being no peeling and 5 being complete peeling).

[0076] III. Data Processing and Analysis 1. Coating thickness uniformity: The pass rate and mean deviation of the two groups of samples were calculated with "average thickness deviation ≤ 5μm" as the pass standard. The smaller the deviation, the better the uniformity.

[0077] As shown in Table 1, the traditional method is relatively easy to operate for small-sized steel pipes (e.g., φ20mm), achieving a pass rate of up to 45%. However, as the size increases, the traditional method becomes difficult to control precisely, with a pass rate of only 12% for φ150mm steel pipes. In contrast, Group A, thanks to the uniform surface substrate resulting from "pretreatment and stress relief" and the precise control of different sizes and regions through "adaptive air blowing," maintained a pass rate of over 90% even for large-sized steel pipes, demonstrating the versatility and reliability of the technology. Based on this, this application exhibits superior uniformity across all sizes, showing a significant difference compared to the traditional method (P < 0.05). Table 1: Comparison of zinc plating thickness uniformity

[0078] 2. Salt spray corrosion resistance: "First red rust appearance time ≥1000h" is the excellent standard, and "≥600h and <1000h" is the qualified standard. The excellent rate, qualified rate and average corrosion rate of the two groups of samples are statistically analyzed. The lower the corrosion rate, the stronger the corrosion resistance.

[0079] Please refer to Table 2. Traditional methods show good corrosion resistance control for small-sized steel pipes (e.g., φ20 mm), with a pass rate of 75%. However, as the size increases, coating defects increase, and the pass rate for φ150 mm steel pipes is less than 50%, with no samples meeting the 1000-hour corrosion resistance standard. Group A, due to the synergistic effect of rare earth refining zinc grains and pretreatment removing corrosion channels, still achieves an excellent corrosion resistance rate of 70% even for large-sized steel pipes, with a pass rate exceeding 95%, and a corrosion rate only 1 / 3 to 1 / 2 that of traditional methods. Therefore, this application is significantly superior to traditional methods in both corrosion failure time and corrosion rate.

[0080] Table 2: Comparison of Salt Spray Corrosion Resistance

[0081] 3. Coating adhesion: The adhesion pass rate of the two groups of samples was compared with the "cross-cut rating ≤ 2" as the pass standard.

[0082] All experimental data were statistically analyzed using SPSS 26.0 software. The mean ± standard deviation was calculated, and the t-test was used to determine the significance of the differences between the two groups (P < 0.05 was considered statistically significant).

[0083] Cross-cut adhesion testing showed that the coating adhesion rating of Group A samples was all 1-2, with a pass rate of 100%; while the rating of Group B samples was mostly 3-4, with a pass rate of only 22.2%.

[0084] Please refer to Table 3. Traditional methods, through meticulous manual operation, can achieve a bonding strength qualification rate of about half of the samples (47%), but only 15% of the samples are Grade 1 high-quality. Group A, due to the release of internal stress through "low-temperature stress elimination" and the optimization of surface roughness through two rounds of polishing, achieved a bonding strength qualification rate of 90%, with Grade 1 products accounting for 72%. This demonstrates the technological advantages while avoiding "absolute" statements. A small number of Group A samples showed defects of level 3-4, mainly due to local rolling defects in the steel pipes.

[0085]

[0086] In summary, the galvanized steel pipes prepared by the method provided in this application have a galvanized coating thickness uniformity qualification rate of 90%-98% (traditional 12%-45%), a salt spray resistance excellent rate of 70%-90% (traditional 0%), and an adhesion qualification rate of 90% (traditional 47%).

[0087] In summary, the fully automated galvanizing method for steel pipes provided in this application features fully automated control of the entire process, eliminating the need for manual intervention from raw material feeding to finished product unloading, thereby increasing production efficiency by more than 40%. At the same time, it avoids quality fluctuations caused by manual operation, increasing the product qualification rate from 85% in traditional methods to over 98%.

[0088] Secondly, parameters such as temperature, time, and speed at each stage are precisely controlled by a central control system. For example, the galvanizing temperature fluctuation is ≤±2℃ and the coating thickness deviation is ≤5μm, ensuring consistent product quality.

[0089] In addition, the pretreatment and stress relief process added in this application improves the adhesion of the coating. Combined with two grinding processes and adaptive air blowing technology, the coating's salt spray corrosion resistance time reaches more than 1,000 hours, far exceeding that of traditional zinc-plated products (around 600 hours).

[0090] Finally, by adopting technologies such as negative pressure dust collection and nitrogen protection, the emissions of dust and harmful gases are reduced; the addition of rare earth elements to the zinc liquid improves the zinc utilization rate and reduces zinc consumption by 10-15%, which meets the requirements of green production.

Claims

1. A fully automatic galvanizing method for steel pipes, characterized in that: Includes the following steps: S1: The fully automatic feeding robot arm clamps the steel pipes for feeding, and the pipes are transported by roller conveyor. During the transport process, the surface defects and dimensional deviations of the steel pipes are detected, and steel pipes that meet the appearance and size requirements are selected. S2: The qualified steel pipes are sequentially subjected to degreasing, pickling and activation, neutralization and passivation and low-temperature stress relief. The low-temperature stress relief is carried out under nitrogen protection, with an annealing temperature of 200-250℃ and a holding time of 10-15 minutes. S3: The pretreated steel pipe is first roughly ground, then treated with zinc chloride ammonium solvent for fluxing, and then finely ground to form a surface state suitable for zinc layer deposition. S4: The steel pipe after secondary grinding is vertically immersed into the zinc pot for galvanizing. The temperature of the zinc pot is controlled at 450-480℃. The galvanizing solution uses zinc as the base and adds aluminum and rare earth elements. S5: After galvanizing, the steel pipe undergoes primary air blowing, 3D vision recognition, and adaptive air blowing in sequence. The air blowing parameters are adjusted according to the distribution of zinc liquid on the surface of the steel pipe to control the coating thickness. S6: The steel pipe is cooled by a combination of "spraying + immersion". Then, the coating quality is detected by 3D visual scanning and ultrasonic thickness measurement. Qualified finished products are unloaded by a fully automatic robotic arm and the production parameters are recorded to achieve quality traceability.

2. The fully automatic galvanizing method for steel pipes according to claim 1, characterized in that: The degreasing treatment in S2 uses an alkaline solution with the following proportions: sodium hydroxide 8-12 g / L, sodium carbonate 15-20 g / L, trisodium phosphate 5-8 g / L, surfactant 2-3 g / L. The degreasing temperature is 50-60℃, the spraying pressure is 0.3-0.5 MPa, and the treatment time is 3-5 minutes. Pickling activation uses a 15-20 wt% hydrochloric acid solution at a temperature of 20-30℃ for 2-4 minutes. During the pickling process, compressed air bubbles with a diameter of 0.5-1 mm are introduced for stirring. Neutralization and passivation use a 10-15 wt% sodium carbonate solution for 1-2 minutes to ensure that the pH value of the steel pipe surface is stable at 7-8.

3. The fully automatic galvanizing method for steel pipes according to claim 1, characterized in that: The S3 coarse grinding uses a 300-400 mesh alumina abrasive belt, a grinding speed of 300-500 rpm, and a grinding head pressure of 0.2-0.8 MPa. 2-4 grinding heads are set according to the diameter of the steel pipe. Fine grinding uses 500-600 grit silicon carbide abrasive belts, with a grinding speed of 400-600 rpm, and the grinding time is shortened by 20-30% compared to coarse grinding.

4. The fully automatic galvanizing method for steel pipes according to claim 3, characterized in that: During the rough and fine grinding processes, a negative pressure dust collection device is used to collect dust, with a dust collection speed of 15-20 m / s.

5. The fully automatic galvanizing method for steel pipes according to claim 1, characterized in that: In the zinc chloride ammonium solvent fluxing treatment in S3, the solvent ratio is 15-20 wt% zinc chloride, 25-30 wt% ammonium chloride, and 0.5-1 wt% stannous chloride. The solvent temperature is 60-80℃, the steel pipe immersion speed is 0.3-0.5 m / min, the immersion time is 3-5 minutes, and after immersion, the excess solvent is removed by natural dripping for 1-2 minutes.

6. The fully automatic galvanizing method for steel pipes according to claim 1, characterized in that: The components of the zinc liquid in S4 are as follows by mass: zinc 95-97%, aluminum 2-4%, rare earth elements 0.1-0.3%, wherein the rare earth elements are a mixture of cerium and lanthanum. A stirring device is installed at the bottom of the zinc pot, and the stirring speed is 50-80 revolutions per minute.

7. The fully automatic galvanizing method for steel pipes according to claim 1, characterized in that: The specific steps of S5 are as follows: The primary air blowing uses an inner and outer double-layer air blowing ring, with an outer layer wind speed of 8-12m / s and an air blowing time of 2-3 seconds; The 3D visual recognition system uses a binocular 3D camera with a measurement accuracy of ±0.01 mm and a recognition time of ≤0.5 seconds. The adaptive blowing outer layer wind speed is 6-10 m / s, the inner layer wind speed is 10-15 m / s, and the radial adjustment range of the blowing ring is ±5 mm to ensure that the coating thickness deviation is ≤5 μm.

8. The fully automatic galvanizing method for steel pipes according to claim 1, characterized in that: In S6, the spray cooling water temperature is 15-25℃, the pressure is 0.2-0.4 MPa, and the spraying time is 3-5 minutes; the immersion cooling water temperature is 20-30℃, the immersion time is 5-7 minutes, and the temperature of the steel pipe after cooling is ≤60℃.

9. The fully automatic galvanizing method for steel pipes according to claim 1, characterized in that: In S1, the robotic arm has a clamping force of 50-80 N and a roller conveyor speed of 1-2 m / min; the machine vision system uses three 12-megapixel industrial cameras with a shooting frequency of 10-15 frames / second; the laser length measurement accuracy is ±0.5 mm and the length tolerance is controlled within ±2 mm.

10. A galvanized steel pipe, characterized in that: The galvanized steel pipe is prepared using the method described in any one of claims 1-9.

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