CN110904399A - Hot-dip galvanizing process for high-strength steel pipe - Google Patents
Hot-dip galvanizing process for high-strength steel pipe Download PDFInfo
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- CN110904399A CN110904399A CN201911217690.5A CN201911217690A CN110904399A CN 110904399 A CN110904399 A CN 110904399A CN 201911217690 A CN201911217690 A CN 201911217690A CN 110904399 A CN110904399 A CN 110904399A
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/38—Wires; Tubes
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/24—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/04—Cleaning or pickling metallic material with solutions or molten salts with acid solutions using inhibitors
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
- C23G1/081—Iron or steel solutions containing H2SO4
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Abstract
The invention discloses a hot-dip galvanizing process for a high-strength steel pipe, which specifically comprises the following steps: s1, degreasing; s2, acid washing; s3, dipping plating assistant agent; s4, drying and preheating; s5, hot galvanizing; s6, finishing and plating; s7, passivating; s8, cooling; s9, checking; the plated part prepared by the hot galvanizing process has good uniformity, strong corrosion resistance and bright and beautiful plating layer, and simultaneously reduces the consumption of zinc liquid and heat energy, thereby effectively reducing the cost, reducing the generation of zinc ash and zinc slag and improving the quality of the plated part; according to the invention, through the addition of the fog inhibitor, on one hand, corrosion possibly caused during acid washing of the plated part is reduced, on the other hand, the generation of acid mist during acid washing is inhibited, so that corrosion to a galvanizing workshop is avoided, and meanwhile, the working environment of galvanizing personnel is improved; the invention strictly reduces the erosion of the zinc liquid to the workpiece and the zinc pot by controlling the temperature of the zinc liquid.
Description
Technical Field
The invention relates to the field of steel pipe processing, in particular to a hot-dip galvanizing process for a high-strength steel pipe.
Background
The steel pipe has a hollow cross section with a length much greater than the diameter or circumference of the steel. The steel pipe is divided into round, square, rectangular and special-shaped steel pipes according to the shape of the cross section; the steel pipe is divided into a carbon structural steel pipe, a low-alloy structural steel pipe, an alloy steel pipe and a composite steel pipe according to the material quality; the steel pipes are divided into steel pipes for conveying pipelines, engineering structures, thermal equipment, petrochemical industry, machinery manufacturing, geological drilling, high-pressure equipment and the like according to the application; the production process includes seamless steel pipe and welded steel pipe, the seamless steel pipe includes hot rolling and cold rolling (drawing), and the welded steel pipe includes straight seam welded steel pipe and spiral seam welded steel pipe.
Steel pipes are not only used for transporting fluids and powdery solids, exchanging heat energy, manufacturing mechanical parts and containers, but also are economical steels. The steel pipe is used for manufacturing the building structure net rack, the supporting column and the mechanical support, so that the weight can be reduced, the metal can be saved by 20-40%, and the industrialized mechanized construction can be realized. The steel pipe is used for manufacturing the highway bridge, so that steel can be saved, the construction is simplified, the area of a coating protective layer can be greatly reduced, and the investment and the maintenance cost are saved.
Hot dip galvanizing, also known as hot dip galvanizing, is a method of dipping steel members into a molten zinc bath to obtain a metal coating. In recent years, along with the rapid development of high-voltage power transmission, traffic and communication industries, the protection requirements on steel parts are higher and higher, and the demand of hot galvanizing is also continuously increased.
Disclosure of Invention
The invention aims to provide a hot-dip galvanizing process for a high-strength steel pipe, which aims to solve the problems in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme:
a hot-dip galvanizing process for a high-strength steel pipe specifically comprises the following steps:
s1, degreasing:
chemical degreasing or water-based metal degreasing cleaning agent is adopted for degreasing until the workpiece is completely soaked in water;
s2, acid washing:
by means of H2SO415 percent of thiourea, 0.1 percent of thiourea, or pickling with HCl20 percent, 3-5 g/L of urotropine at the temperature of 40-60 ℃ at the temperature of 20-40 ℃; the corrosion inhibitor is added to prevent the over-corrosion of the matrix and reduce the hydrogen absorption amount of the iron matrix, and the fog inhibitor is added to inhibit the escape of acid mist; poor adhesion of the plating layer, no zinc plating or zinc layer falling off can be caused by poor degreasing and acid pickling;
s3, dipping plating assistant agent:
is also calledThe solvent can keep the workpiece to have certain activity before dip plating so as to avoid secondary oxidation and enhance the combination of the plating layer and the matrix; NH (NH)4Cl 100-150g/L，ZnCl2150-; and adding a certain amount of explosion-proof agent;
s4, drying and preheating:
preheating is generally 80-140 ℃ in order to prevent the workpiece from deforming due to rapid temperature rise during immersion plating, remove residual moisture and prevent zinc explosion and zinc liquid explosion splashing;
s5, hot galvanizing:
controlling the temperature of the zinc liquid, the dip plating time and the speed of leading the workpiece out of the zinc liquid; the extraction speed is generally 1.5 m/min; the temperature is too low, the fluidity of the zinc liquid is poor, the plating layer is thick and uneven, sagging is easy to generate, and the appearance quality is poor; the temperature is high, the fluidity of the zinc liquid is good, the zinc liquid is easy to separate from a workpiece, the phenomena of sagging and wrinkling are reduced, the adhesive force is strong, the coating is thin, the appearance is good, and the production efficiency is high; however, the temperature is too high, the iron loss of the workpiece and the zinc pot is serious, a large amount of zinc slag is generated, the quality of a zinc dipping layer is influenced, color difference is easy to cause, the surface color is unsightly, and the zinc consumption is high;
s6, sorting:
after plating, the workpiece is finished by mainly removing residual zinc and zinc nodules on the surface and adopting a vibrator special for hot galvanizing;
s7, passivation:
aims to improve the atmospheric corrosion resistance of the surface of a workpiece, reduce or prolong the occurrence time of white rust and keep a plating layer to have good appearance; chromate is used for passivation, such as Na2Cr2O 780-100 g/L and sulfuric acid 3-4 ml/L, but the passivation solution seriously affects the environment, and preferably chromium-free passivation is adopted;
s8, cooling:
water cooling is generally used, but the temperature can not be too low or too high, generally not lower than 30 ℃ and not higher than 70 ℃,
s9, checking:
the coating has bright and delicate appearance and no sagging and wrinkling phenomena;
the thickness test adopts a coating thickness gauge, and the method is simple and convenient; the thickness of the plating layer can also be obtained by converting the zinc adhesion amount;
bending the sample piece by a bending press machine for 90-180 degrees in combination strength, wherein the sample piece is free from cracks and coating falling off; the test was also carried out by hammer impact test and the salt spray test and the copper sulfate etching test were carried out in batches.
Further, the pickling solution in the step S2 is further added with a fog inhibitor, the addition amount of the fog inhibitor is 0.1% -1.5%, and the fog inhibitor comprises the following raw materials in parts by weight: 4-10% of nonionic surfactant, 8-15% of amine organic matter and the balance of water.
Further, the nonionic surfactant is one or more of octyl phenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, high-carbon fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ester, fatty acid methyl ester ethoxylate, polyether nonionic surfactant, fatty acid sorbitan ester and sucrose fatty acid ester; the amine organic matter is one or more of aniline, ethylenediamine, triethanolamine, acetamide and cyclohexylamine.
Further, the pH value of the S3 plating assistant is maintained at 5, the plating assistant is an aqueous solution prepared from zinc chloride and ammonia chloride, the working temperature is 60-80 ℃, and the working concentration is 80-150 g/L.
Further, the working temperature of the zinc liquid in the step S5 is in two regions of 450-480 ℃ and 520-560 ℃.
Further, the working temperature of the zinc liquid in the step S5 is controlled to 455-465 ℃ when plating a plated piece made of Q235 material; plating a plating piece made of the Q345 material, and controlling the temperature at 465-480 ℃; keeping the temperature of 425 ℃ and 435 ℃ during the production stop period; the hot-dip galvanizing time is that the part with the thickness less than 5mm is subjected to hot dipping for 50-60 s; soaking the part with the thickness of 5-8mm in zinc for 60-80 s; soaking the part with the thickness more than 8mm in zinc for 70-90 s; the tower foot is 120-150 s.
Further, the zinc pot material of the step S5 is 08F high-quality carbon steel plate which contains 0.087 percent of carbon (0.05 percent to 0.11 percent) and less than or equal to 0.03 percent of silicon and contains elements such as nickel, chromium and the like capable of inhibiting iron from being etched.
In step S5, the temperature is increased to the upper limit of the process temperature to separate the zinc dross from the molten zinc, and then decreased to a temperature below the process temperature to allow the zinc dross to settle at the bottom of the bath and then be scooped up with a spoon, and the plated part falling into the molten zinc is also timely scooped up.
Compared with the prior art, the invention has the beneficial effects that:
the plated part prepared by the hot galvanizing process has good uniformity, strong corrosion resistance and bright and beautiful plating layer, and simultaneously reduces the consumption of zinc liquid and heat energy, thereby effectively reducing the cost, reducing the generation of zinc ash and zinc slag and improving the quality of the plated part;
according to the invention, through the addition of the fog inhibitor, on one hand, corrosion possibly caused during acid washing of the plated part is reduced, on the other hand, the generation of acid mist during acid washing is inhibited, so that corrosion to a galvanizing workshop is avoided, and meanwhile, the working environment of galvanizing personnel is improved;
the invention strictly reduces the erosion of the zinc liquid to the workpiece and the zinc pot by controlling the temperature of the zinc liquid.
Detailed Description
The technical solution of the present patent will be described in further detail with reference to the following embodiments.
In the first embodiment, a hot-dip galvanizing process for a high-strength steel pipe specifically comprises the following steps:
s1, degreasing:
chemical degreasing or water-based metal degreasing cleaning agent is adopted for degreasing until the workpiece is completely soaked in water;
s2, acid washing:
by means of H2SO415 percent of thiourea, 0.1 percent of thiourea, or pickling with HCl20 percent, 3-5 g/L of urotropine at the temperature of 40-60 ℃ at the temperature of 20-40 ℃; the corrosion inhibitor is added to prevent the over-corrosion of the matrix and reduce the hydrogen absorption amount of the iron matrix, and the fog inhibitor is added to inhibit the escape of acid mist; poor adhesion of the plating layer, no zinc plating or zinc layer falling off can be caused by poor degreasing and acid pickling;
s3, dipping plating assistant agent:
also called solvent, can keep the workpiece to have certain activity before dip plating to avoid secondary oxidation so as to enhance the combination of the plating layer and the matrix; NH (NH)4Cl 100-150g/L，ZnCl2150-; and addAdding a certain amount of explosion-proof agent;
s4, drying and preheating:
preheating is generally 80-140 ℃ in order to prevent the workpiece from deforming due to rapid temperature rise during immersion plating, remove residual moisture and prevent zinc explosion and zinc liquid explosion splashing;
s5, hot galvanizing:
controlling the temperature of the zinc liquid, the dip plating time and the speed of leading the workpiece out of the zinc liquid; the extraction speed is generally 1.5 m/min; the temperature is too low, the fluidity of the zinc liquid is poor, the plating layer is thick and uneven, sagging is easy to generate, and the appearance quality is poor; the temperature is high, the fluidity of the zinc liquid is good, the zinc liquid is easy to separate from a workpiece, the phenomena of sagging and wrinkling are reduced, the adhesive force is strong, the coating is thin, the appearance is good, and the production efficiency is high; however, the temperature is too high, the iron loss of the workpiece and the zinc pot is serious, a large amount of zinc slag is generated, the quality of a zinc dipping layer is influenced, color difference is easy to cause, the surface color is unsightly, and the zinc consumption is high;
s6, sorting:
after plating, the workpiece is finished by mainly removing residual zinc and zinc nodules on the surface and adopting a vibrator special for hot galvanizing;
s7, passivation:
aims to improve the atmospheric corrosion resistance of the surface of a workpiece, reduce or prolong the occurrence time of white rust and keep a plating layer to have good appearance; chromate is used for passivation, such as Na2Cr2O 780-100 g/L and sulfuric acid 3-4 ml/L, but the passivation solution seriously affects the environment, and preferably chromium-free passivation is adopted;
s8, cooling:
water cooling is generally used, but the temperature can not be too low or too high, generally not lower than 30 ℃ and not higher than 70 ℃,
s9, checking:
the coating has bright and delicate appearance and no sagging and wrinkling phenomena;
the thickness test adopts a coating thickness gauge, and the method is simple and convenient; the thickness of the plating layer can also be obtained by converting the zinc adhesion amount;
bending the sample piece by a bending press machine for 90-180 degrees in combination strength, wherein the sample piece is free from cracks and coating falling off; the test can also be carried out by heavy hammer knocking test, and the salt spray test and the copper sulfate etching test are carried out in batches;
the formation of zinc dross in the zinc bath is mainly a zinc-iron alloy with extremely poor fluidity formed when the iron content dissolved in the zinc bath exceeds the solubility at the temperature, and the zinc content in the zinc dross can reach 95 percent, which is the key point of high hot galvanizing cost.
From the solubility curve of iron in zinc bath, it can be seen that: the iron dissolving amount, i.e. the iron loss amount, is different at different temperatures and different heat preservation times. At around 500 ℃, the iron loss increases sharply with the heating and holding time, and is almost linear. The temperature is lower than or higher than 480-510 ℃, and the iron loss is slowly increased along with the time extension. Therefore, 480 to 510 ℃ is called a malignant dissolution region. In the temperature range, the zinc liquid has the most serious erosion to workpieces and zinc pots, the iron loss is obviously increased when the temperature is higher than 560 ℃, the zinc is destructively eroded to an iron matrix when the temperature is higher than 660 ℃, the zinc slag is rapidly increased, and the plating cannot be carried out. Therefore, the plating is currently performed in two regions of 450-480 ℃ and 520-560 ℃.
The working temperature of the zinc liquid is controlled at 455-465 ℃ when plating a plating piece made of Q235 material; plating a plating piece made of the Q345 material, and controlling the temperature at 465-480 ℃; keeping the temperature of 425 ℃ and 435 ℃ during the production stop period; the hot-dip galvanizing time is that the part with the thickness less than 5mm is subjected to hot dipping for 50-60 s; soaking the part with the thickness of 5-8mm in zinc for 60-80 s; soaking the part with the thickness more than 8mm in zinc for 70-90 s; the tower foot is 120-150 s.
The reduction of the zinc slag is to reduce the iron content in the zinc liquid, and the reduction of the iron dissolution is started by the following factors:
the plating and heat preservation need to avoid the dissolution peak area of iron, namely, the operation is not carried out at 480-510 ℃,
the material of the zinc pot is welded by steel plates containing carbon and low silicon as far as possible, the carbon content is high, the corrosion of zinc liquid to the iron pot is accelerated, the silicon content is high, and the corrosion of the zinc liquid to the iron can also be promoted, at present, a 08F high-quality carbon steel plate is mostly adopted, the carbon content is 0.087 percent (0.05-0.11 percent), the silicon content is less than or equal to 0.03 percent, and the steel plate contains elements such as nickel, chromium and the like capable of inhibiting the iron corrosion.
The zinc ash zinc slag not only seriously affects the quality of a zinc dipping layer to cause rough coating and zinc nodules, but also greatly increases the hot galvanizing cost, the zinc consumption of a workpiece is usually 80-120 kg per 1t of plated workpiece, if the zinc ash zinc slag is serious, the zinc consumption can be as high as 140-200 kg,
the zinc and carbon are controlled to well control the temperature, the scum generated by the oxidation of the surface of the zinc liquid is reduced,
the temperature is increased to the upper limit of the process temperature so as to separate the zinc slag from the zinc liquid, then the temperature is reduced to be lower than the process temperature, the zinc slag is settled at the bottom of the tank and then fished by a spoon, the plated part falling into the zinc liquid is fished in time,
in order to prevent iron in the plating assistant agent from being brought into a zinc bath along with a workpiece, a red brown iron-containing compound is generated when the plating assistant agent is used for a certain time, the iron-containing compound is filtered out periodically, and the pH value of the plating assistant agent is maintained at 5.
The generation of sediment can be accelerated when the aluminum content in the plating solution is less than 0.01 percent, the proper amount of aluminum not only improves the fluidity of zinc liquid and increases the brightness of a plating layer, but also is beneficial to reducing zinc slag and zinc ash, a small amount of aluminum floats on the liquid surface to reduce oxidation, the quality of the plating layer is influenced too much, and the phenomenon of spot defect is generated,
the heating and the temperature rise are uniform, and the explosion and the local overheating are prevented.
In the second embodiment, a hot-dip galvanizing process for a high-strength steel pipe specifically includes the following steps:
s1, degreasing:
chemical degreasing or water-based metal degreasing cleaning agent is adopted for degreasing until the workpiece is completely soaked in water;
s2, acid washing:
by means of H2SO415 percent of thiourea, 0.1 percent of thiourea, or pickling with HCl20 percent, 3-5 g/L of urotropine at the temperature of 40-60 ℃ at the temperature of 20-40 ℃; the corrosion inhibitor is added to prevent the over-corrosion of the matrix and reduce the hydrogen absorption amount of the iron matrix, and the fog inhibitor is added to inhibit the escape of acid mist; poor adhesion of the plating layer, no zinc plating or zinc layer falling off can be caused by poor degreasing and acid pickling;
s3, dipping plating assistant agent:
also called solvent, can keep the workpiece to have certain activity before dip plating to avoid secondary oxidation so as to enhance the combination of the plating layer and the matrix; NH (NH)4Cl 100-150g/L，ZnCl2150-; and adding a certain amount of explosion-proof agent;
s4, drying and preheating:
preheating is generally 80-140 ℃ in order to prevent the workpiece from deforming due to rapid temperature rise during immersion plating, remove residual moisture and prevent zinc explosion and zinc liquid explosion splashing;
s5, hot galvanizing:
controlling the temperature of the zinc liquid, the dip plating time and the speed of leading the workpiece out of the zinc liquid; the extraction speed is generally 1.5 m/min; the temperature is too low, the fluidity of the zinc liquid is poor, the plating layer is thick and uneven, sagging is easy to generate, and the appearance quality is poor; the temperature is high, the fluidity of the zinc liquid is good, the zinc liquid is easy to separate from a workpiece, the phenomena of sagging and wrinkling are reduced, the adhesive force is strong, the coating is thin, the appearance is good, and the production efficiency is high; however, the temperature is too high, the iron loss of the workpiece and the zinc pot is serious, a large amount of zinc slag is generated, the quality of a zinc dipping layer is influenced, color difference is easy to cause, the surface color is unsightly, and the zinc consumption is high;
s6, sorting:
after plating, the workpiece is finished by mainly removing residual zinc and zinc nodules on the surface and adopting a vibrator special for hot galvanizing;
s7, passivation:
aims to improve the atmospheric corrosion resistance of the surface of a workpiece, reduce or prolong the occurrence time of white rust and keep a plating layer to have good appearance; chromate is used for passivation, such as Na2Cr2O 780-100 g/L and sulfuric acid 3-4 ml/L, but the passivation solution seriously affects the environment, and preferably chromium-free passivation is adopted;
s8, cooling:
water cooling is generally used, but the temperature can not be too low or too high, generally not lower than 30 ℃ and not higher than 70 ℃,
s9, checking:
the coating has bright and delicate appearance and no sagging and wrinkling phenomena;
the thickness test adopts a coating thickness gauge, and the method is simple and convenient; the thickness of the plating layer can also be obtained by converting the zinc adhesion amount;
bending the sample piece by a bending press machine for 90-180 degrees in combination strength, wherein the sample piece is free from cracks and coating falling off; the test can also be carried out by heavy hammer knocking test, and the salt spray test and the copper sulfate etching test are carried out in batches;
the formation of zinc dross in the zinc bath is mainly a zinc-iron alloy with extremely poor fluidity formed when the iron content dissolved in the zinc bath exceeds the solubility at the temperature, and the zinc content in the zinc dross can reach 95 percent, which is the key point of high hot galvanizing cost.
From the solubility curve of iron in zinc bath, it can be seen that: the iron dissolving amount, i.e. the iron loss amount, is different at different temperatures and different heat preservation times. At around 500 ℃, the iron loss increases sharply with the heating and holding time, and is almost linear. The temperature is lower than or higher than 480-510 ℃, and the iron loss is slowly increased along with the time extension. Therefore, 480 to 510 ℃ is called a malignant dissolution region. In the temperature range, the zinc liquid has the most serious erosion to workpieces and zinc pots, the iron loss is obviously increased when the temperature is higher than 560 ℃, the zinc is destructively eroded to an iron matrix when the temperature is higher than 660 ℃, the zinc slag is rapidly increased, and the plating cannot be carried out. Therefore, the plating is currently performed in two regions of 450-480 ℃ and 520-560 ℃.
The working temperature of the zinc liquid is controlled at 455-465 ℃ when plating a plating piece made of Q235 material; plating a plating piece made of the Q345 material, and controlling the temperature at 465-480 ℃; keeping the temperature of 425 ℃ and 435 ℃ during the production stop period; the hot-dip galvanizing time is that the part with the thickness less than 5mm is subjected to hot dipping for 50-60 s; soaking the part with the thickness of 5-8mm in zinc for 60-80 s; soaking the part with the thickness more than 8mm in zinc for 70-90 s; the tower foot is 120-150 s.
The reduction of the zinc slag is to reduce the iron content in the zinc liquid, and the reduction of the iron dissolution is started by the following factors:
the plating and heat preservation need to avoid the dissolution peak area of iron, namely, the operation is not carried out at 480-510 ℃,
the material of the zinc pot is welded by steel plates containing carbon and low silicon as far as possible, the carbon content is high, the corrosion of zinc liquid to the iron pot is accelerated, the silicon content is high, and the corrosion of the zinc liquid to the iron can also be promoted, at present, a 08F high-quality carbon steel plate is mostly adopted, the carbon content is 0.087 percent (0.05-0.11 percent), the silicon content is less than or equal to 0.03 percent, and the steel plate contains elements such as nickel, chromium and the like capable of inhibiting the iron corrosion.
The zinc ash zinc slag not only seriously affects the quality of a zinc dipping layer to cause rough coating and zinc nodules, but also greatly increases the hot galvanizing cost, the zinc consumption of a workpiece is usually 80-120 kg per 1t of plated workpiece, if the zinc ash zinc slag is serious, the zinc consumption can be as high as 140-200 kg,
the zinc and carbon are controlled to well control the temperature, the scum generated by the oxidation of the surface of the zinc liquid is reduced,
the temperature is increased to the upper limit of the process temperature so as to separate the zinc slag from the zinc liquid, then the temperature is reduced to be lower than the process temperature, the zinc slag is settled at the bottom of the tank and then fished by a spoon, the plated part falling into the zinc liquid is fished in time,
in order to prevent iron in the plating assistant agent from being brought into a zinc bath along with a workpiece, a red brown iron-containing compound is generated when the plating assistant agent is used for a certain time, the iron-containing compound is filtered out periodically, and the pH value of the plating assistant agent is maintained at 5.
The generation of sediment can be accelerated when the aluminum content in the plating solution is less than 0.01 percent, the proper amount of aluminum not only improves the fluidity of zinc liquid and increases the brightness of a plating layer, but also is beneficial to reducing zinc slag and zinc ash, a small amount of aluminum floats on the liquid surface to reduce oxidation, the quality of the plating layer is influenced too much, and the phenomenon of spot defect is generated,
the heating and the temperature rise are uniform, and the explosion and the local overheating are prevented.
The difference between the embodiment and the first embodiment is that the pickling solution is further added with a mist inhibitor, the addition amount of the mist inhibitor is 0.1-1.5%, and the mist inhibitor comprises the following raw materials in parts by weight: 4-10% of nonionic surfactant, 8-15% of amine organic matter and the balance of water.
The nonionic surfactant is one or more of octyl phenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, high-carbon fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ester, fatty acid methyl ester ethoxylate, polyether nonionic surfactant, fatty acid sorbitan ester and sucrose fatty acid ester; the amine organic matter is one or more of aniline, ethylenediamine, triethanolamine, acetamide and cyclohexylamine.
The plating assistant agent is water solution prepared from zinc chloride and ammonia chloride, the working temperature is 60-80 ℃, and the working concentration is 80-150 g/L.
Although the preferred embodiments of the present patent have been described in detail, the present patent is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present patent within the knowledge of those skilled in the art.
Claims (8)
1. A hot-dip galvanizing process for a high-strength steel pipe specifically comprises the following steps:
s1, degreasing:
chemical degreasing or water-based metal degreasing cleaning agent is adopted for degreasing until the workpiece is completely soaked in water;
s2, acid washing:
particularly by H2SO415 percent of thiourea, 0.1 percent of thiourea, or pickling with HCl20 percent, 3-5 g/L of urotropine at the temperature of 40-60 ℃ at the temperature of 20-40 ℃; the corrosion inhibitor is added to prevent the over-corrosion of the matrix and reduce the hydrogen absorption amount of the iron matrix, and the fog inhibitor is added to inhibit the escape of acid mist; poor adhesion of the plating layer, no zinc plating or zinc layer falling off can be caused by poor degreasing and acid pickling;
s3, dipping plating assistant agent:
the dipping plating assistant agent is used for keeping the workpiece to have certain activity before dipping plating so as to avoid secondary oxidation and enhance the combination of a plating layer and a matrix; NH (NH)4Cl 100-150g/L，ZnCl2150-; and adding a certain amount of explosion-proof agent;
s4, drying and preheating:
preheating is generally 80-140 ℃ in order to prevent the workpiece from deforming due to rapid temperature rise during immersion plating, remove residual moisture and prevent zinc explosion and zinc liquid explosion splashing;
s5, hot galvanizing:
controlling the temperature of the zinc liquid, the dip plating time and the speed of leading the workpiece out of the zinc liquid; the extraction speed is generally 1.5 m/min; the temperature is too low, the fluidity of the zinc liquid is poor, the plating layer is thick and uneven, sagging is easy to generate, and the appearance quality is poor; the temperature is high, the fluidity of the zinc liquid is good, the zinc liquid is easy to separate from a workpiece, the phenomena of sagging and wrinkling are reduced, the adhesive force is strong, the coating is thin, the appearance is good, and the production efficiency is high; however, the temperature is too high, the iron loss of the workpiece and the zinc pot is serious, a large amount of zinc slag is generated, the quality of a zinc dipping layer is influenced, color difference is easy to cause, the surface color is unsightly, and the zinc consumption is high;
s6, sorting:
after plating, the workpiece is finished by mainly removing residual zinc and zinc nodules on the surface and adopting a vibrator special for hot galvanizing;
s7, passivation:
aims to improve the atmospheric corrosion resistance of the surface of a workpiece, reduce or prolong the occurrence time of white rust and keep a plating layer to have good appearance; chromate is used for passivation, such as Na2Cr2O 780-100 g/L and sulfuric acid 3-4 ml/L, but the passivation solution seriously affects the environment, and preferably chromium-free passivation is adopted;
s8, cooling:
water cooling is generally used, but the temperature can not be too low or too high, generally not lower than 30 ℃ and not higher than 70 ℃,
s9, checking:
the coating has bright and delicate appearance and no sagging and wrinkling phenomena;
the thickness test adopts a coating thickness gauge, and the method is simple and convenient; the thickness of the plating layer can also be obtained by converting the zinc adhesion amount;
bending the sample piece by a bending press machine for 90-180 degrees in combination strength, wherein the sample piece is free from cracks and coating falling off; the test was also carried out by hammer impact test and the salt spray test and the copper sulfate etching test were carried out in batches.
2. Further, the pickling solution in the step S2 is further added with a fog inhibitor, the addition amount of the fog inhibitor is 0.1% -1.5%, and the fog inhibitor comprises the following raw materials in parts by weight: 4-10% of nonionic surfactant, 8-15% of amine organic matter and the balance of water.
3. The hot-dip galvanizing process for high-strength steel pipes according to claim 2, wherein the nonionic surfactant is one or more of octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, high-carbon fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ester, fatty acid methyl ester ethoxylate, polyether nonionic surfactant, fatty acid sorbitan ester, and sucrose fatty acid ester; the amine organic matter is one or more of aniline, ethylenediamine, triethanolamine, acetamide and cyclohexylamine.
4. The hot-dip galvanizing process for high-strength steel pipes according to claim 1, wherein the pH of the plating assistant agent is maintained at 5 in step S3, the plating assistant agent is an aqueous solution prepared from zinc chloride and ammonia chloride, the working temperature is 60-80 ℃, and the working concentration is 80-150 g/l.
5. The hot-dip galvanizing process for high-strength steel pipes as claimed in claim 1, wherein the operating temperature of the molten zinc in step S5 is in the range of 450-480 ℃ and 520-560 ℃.
6. The hot-dip galvanizing process for high-strength steel pipes as claimed in claim 1, wherein the working temperature of the molten zinc in the step S5 is controlled to 455-465 ℃ when plating Q235 material; plating a plating piece made of the Q345 material, and controlling the temperature at 465-480 ℃; keeping the temperature of 425 ℃ and 435 ℃ during the production stop period; the hot-dip galvanizing time is that the part with the thickness less than 5mm is subjected to hot dipping for 50-60 s; soaking the part with the thickness of 5-8mm in zinc for 60-80 s; soaking the part with the thickness more than 8mm in zinc for 70-90 s; the tower foot is 120-150 s.
7. The hot-dip galvanizing process for high-strength steel pipes according to claim 1, wherein the zinc pot material of step S5 is a 08F high-quality carbon steel plate containing 0.087% (0.05-0.11%) carbon, 0.03% silicon and containing elements such as nickel, chromium, etc. that can inhibit iron corrosion.
8. The hot-dip galvanizing process for high-strength steel pipes as claimed in claim 1, wherein the slag is frequently removed in step S5, the temperature is raised to the upper limit of the process temperature to separate the zinc slag from the molten zinc, and then the temperature is lowered to a temperature lower than the process temperature, so that the zinc slag is settled on the bottom of the steel pipe and then removed by a spoon, and the plated parts falling into the molten zinc are also removed in time.
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| CN111876708A (en) * | 2020-07-15 | 2020-11-03 | 杨吉 | Improved process for reducing zinc consumption of hot-dip galvanized steel pipe by controlling uniformity of zinc layer |
| CN112359305A (en) * | 2020-10-28 | 2021-02-12 | 王倩倩 | Hot galvanizing process for high-strength alloyed steel plate |
| CN112522704A (en) * | 2020-11-27 | 2021-03-19 | 安徽吉利电气设备有限公司 | Corrosion prevention method for stainless steel outdoor power cabinet |
| CN113088853A (en) * | 2021-03-26 | 2021-07-09 | 浙江航峰铁塔有限公司 | Hot galvanizing process for high-strength fastener |
| CN115404425A (en) * | 2022-07-08 | 2022-11-29 | 李宁 | Device for improving coating quality of hot-dip galvanized steel pipe |
| CN117448727A (en) * | 2023-11-07 | 2024-01-26 | 江苏翔宇电力装备制造有限公司 | Hot galvanizing method for iron tower parts of extra-high voltage power transmission and transformation line |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111876708A (en) * | 2020-07-15 | 2020-11-03 | 杨吉 | Improved process for reducing zinc consumption of hot-dip galvanized steel pipe by controlling uniformity of zinc layer |
| CN112359305A (en) * | 2020-10-28 | 2021-02-12 | 王倩倩 | Hot galvanizing process for high-strength alloyed steel plate |
| CN112522704A (en) * | 2020-11-27 | 2021-03-19 | 安徽吉利电气设备有限公司 | Corrosion prevention method for stainless steel outdoor power cabinet |
| CN113088853A (en) * | 2021-03-26 | 2021-07-09 | 浙江航峰铁塔有限公司 | Hot galvanizing process for high-strength fastener |
| CN115404425A (en) * | 2022-07-08 | 2022-11-29 | 李宁 | Device for improving coating quality of hot-dip galvanized steel pipe |
| CN117448727A (en) * | 2023-11-07 | 2024-01-26 | 江苏翔宇电力装备制造有限公司 | Hot galvanizing method for iron tower parts of extra-high voltage power transmission and transformation line |
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