Coating method of high-strength fastener

Abstract

The invention discloses a coating method of a high-strength fastener, which comprises a pre-process and a post-process, the pre-process comprises cleaning, shot blasting, alkaline cyanide-free galvanizing, washing, passivating, washing, sealing and spin-drying, and the post-process comprises cleaning, shot blasting, alkaline cyanide-free galvanizing, washing, passivating, washing, sealing and spin-drying; the post-process comprises the steps of coating, pre-drying, sintering, secondary coating, pre-drying, sintering and blanking. The method has the advantage that the corrosion resistance is improved.

Description

Technical Field

[0001] The invention relates to the field of coating methods, in particular to a coating method for high-strength fasteners. Background Art

[0002] Current high-strength fasteners generally have hydrogen embrittlement problems, and there is a problem of corrosion instability in conventional galvanized conversion films, so there is room for improvement. Summary of the invention

[0003] The object of the present invention is to provide a coating method for high-strength fasteners to solve the problems raised in the above-mentioned background technology, which has the advantage of improving corrosion resistance.

[0004] To achieve the above object, the present invention provides the following technical solution: a coating method for high-strength fasteners, comprising a pre-process and a post-process,

[0005] The previous process includes cleaning, shot blasting, alkaline cyanide-free zinc plating, water washing, passivation, water washing, sealing, and drying;

[0006] The steps include:

[0007] Step 1: Cleaning, pre-treat the substrate, use the cavitation effect, acceleration effect and straight flow effect of ultrasonic waves in 60±5℃ liquid to directly and indirectly act on the liquid and dirt, so that the dirt layer is dispersed, emulsified and peeled off to achieve the purpose of cleaning, and then dry it in a mesh belt at 100-120℃;

[0008] Step 2: Shot blasting: steel shot with a diameter of 0.2mm and a hardness of HRC40-50 is accelerated through the shot blasting wheel to obtain higher kinetic energy, and then sprayed on the surface of the cleaned material for 18-25 minutes to generate impact and friction, clean up the surface oxide scale, rust, dirt and other impurities, improve the surface roughness, enhance the surface adhesion and corrosion resistance of the steel structure, and obtain the pre-treated substrate for standby use;

[0009] Step 3: Alkaline cyanide-free zinc plating, with Zn 2+ The concentration is 6-14g / L, the NaOH concentration is 100-140g / L, the additive is a solution with a ZN-111 content of 8-15ml / L, the pre-treated substrate is placed in the galvanizing tank of the electroplating line, the PLC controls the temperature at 15-35℃, the time is 70-110 minutes, and the current is 0.5-0.75A / dm 2 Then electrolysis is started to reduce the zinc ions to zinc metal on the metal surface, forming a dense zinc layer;

[0010] Step 4: Cleaning: the electroplating line is extracted and transferred to the cleaning tank. The cleaning tank is set for 3-5 seconds, the conductivity is ≤20μS / cm2, and it is cleaned 3 times to make the surface free of dirt;

[0011] Step 5: Passivation, the electroplating line is extracted and transferred to the passivation tank, the passivation solution has a pH value of 1.8-3.2, a temperature of 15-35°C, an A01-435D concentration of 40-80ml / L, and a Zn concentration of ≤10g / L, so that a chromate conversion film is formed on the surface of the zinc layer, reducing the chemical activity of zinc and obtaining better corrosion resistance.

[0012] Step 6: Cleaning: the electroplating line is automatically extracted and transferred to the cleaning tank. The cleaning tank is set for 3-5 seconds, the conductivity is ≤20μS / cm2, and it is cleaned 3 times to make the surface free of dirt;

[0013] Step 7: Sealing, the electroplating line is automatically extracted and transferred to the sealing tank, and the sealing agent ZBT-118 is used, with a concentration of 50-150ml / L, a solution temperature of 35-50℃, and soaked for 8-15S. A protective film is formed by sealing to prevent the metal ions in the electroplating solution from reacting with the surface of the electroplated object, thereby protecting the surface quality and appearance of the electroplated object and increasing the corrosion resistance of the product;

[0014] Step 8: Drying, adjust the parameters of the drying machine, time 10-15 minutes, temperature 70-100℃, speed 400-400 rpm;

[0015] The post-process includes coating, pre-baking, sintering, secondary coating, pre-baking, sintering, and unloading;

[0016] The post-process includes the following steps:

[0017] Step 9: First coating: transfer the electroplated product to the coating line, set the epoxy resin JTF-1082 coating liquid, its viscosity is 20-24S, and the coating liquid temperature is ≤10℃. Through forward and reverse swing for 45 seconds each, the surface is coated with epoxy resin to increase the corrosion resistance of the product;

[0018] Step 10: Pre-baking and sintering. Place the products from step 9 evenly on the mesh belt, set the mesh belt pre-baking temperature to 100-150°C, pre-baking time to 20 minutes, sintering temperature to 210-220°C, sintering time to 20 minutes, and mesh belt speed to 24 cm / min, so that the coating can obtain better bonding strength;

[0019] Step 11: Second coating: After the first coating is sintered, the product is transferred to the coating line, and the epoxy resin JTF-1082 coating liquid is set, the viscosity of which is 20-24S, and the coating liquid temperature is ≤10℃. The epoxy resin coating on the surface is thickened by forward and reverse swaying for 45 seconds each, thereby increasing the corrosion resistance of the product;

[0020] Step 12: Pre-baking and sintering, place the products completed in step 11 evenly on the mesh belt, set the mesh belt pre-baking temperature to 100-150℃, pre-baking time to 20 minutes, sintering temperature to 210-220℃, sintering time to 20 minutes, and mesh belt speed to 24cm / min, so that the coating can obtain better bonding strength.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] Through the composite coating processing method, cleaning + shot blasting is used instead of electroplating pre-treatment. The product does not undergo pickling, which solves the hydrogen embrittlement problem of high-strength fasteners. The zinc-plated layer is used as the primer and epoxy resin is used twice to seal the surface: the salt spray test time is improved, and the corrosion instability problem of conventional zinc-plated conversion film is solved: the actual verification of the salt spray time test effect is increased by about 5 times or more, and the adhesion is also significantly improved. Epoxy resin is used instead of traditional paint or sealant to extend the pre-baking and sintering time of the subsequent process: from appearance to performance improvement. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the embodiment of the present invention,

[0025] Embodiment 1:

[0026] A coating method for high-strength fasteners, including a front process and a back process,

[0027] The previous process includes cleaning, shot blasting, alkaline cyanide-free zinc plating, water washing, passivation, water washing, sealing, and drying;

[0028] The steps include:

[0029] Step 1: Cleaning, pre-treat the substrate, use the cavitation effect, acceleration effect and straight flow effect of ultrasonic waves in 60±5℃ liquid to directly and indirectly act on the liquid and dirt, so that the dirt layer is dispersed, emulsified and peeled off to achieve the purpose of cleaning, and then dry it in a mesh belt at 100-120℃;

[0030] Step 2: Shot blasting: steel shot with a diameter of 0.2mm and a hardness of HRC40-50 is accelerated through the shot blasting wheel to obtain higher kinetic energy, and then sprayed on the surface of the cleaned material for 18-25 minutes to generate impact and friction, clean up the surface oxide scale, rust, dirt and other impurities, improve the surface roughness, enhance the surface adhesion and corrosion resistance of the steel structure, and obtain the pre-treated substrate for standby use;

[0031] Step 3: Alkaline cyanide-free zinc plating, with a Zn2+ concentration of 6g / L, a NaOH concentration of 100g / L, and an additive of 8ml / L of ZN-111. The pre-treated substrate is placed in the zinc plating tank of the electroplating line. The PLC controls the temperature at 15-35°C, the time at 70-110 minutes, and the current at 0.5-0.75A / dm2. Then, electrolysis is started to reduce the zinc ions to zinc metal on the metal surface, forming a dense zinc layer.

[0032] Step 4: Cleaning: the electroplating line is extracted and transferred to the cleaning tank. The cleaning tank is set for 3-5 seconds, the conductivity is ≤20μS / cm2, and it is cleaned 3 times to make the surface free of dirt;

[0033] Step 5: Passivation, the electroplating line is extracted and transferred to the passivation tank, the passivation solution has a pH value of 1.8-3.2, a temperature of 15-35℃, an A01-435D concentration of 40ml / L, and a Zn concentration of ≤10g / L, so that a chromate conversion film is formed on the surface of the zinc layer, reducing the chemical activity of zinc and obtaining better corrosion resistance.

[0034] Step 6: Cleaning: the electroplating line is automatically extracted and transferred to the cleaning tank. The cleaning tank is set for 3-5 seconds, the conductivity is ≤20μS / cm2, and it is cleaned 3 times to make the surface free of dirt;

[0035] Step 7: Sealing, the electroplating line is automatically extracted and transferred to the sealing tank, and the sealing agent ZBT-118 is used, with a concentration of 50ml / L, a solution temperature of 35-50℃, and soaked for 8-15S. A protective film is formed by sealing to prevent the metal ions in the electroplating solution from reacting with the surface of the electroplated object, thereby protecting the surface quality and appearance of the electroplated object and increasing the corrosion resistance of the product;

[0036] Step 8: Drying, adjust the parameters of the drying machine, time 10-15 minutes, temperature 70-100℃, speed 400-400 rpm;

[0037] The post-process includes coating, pre-baking, sintering, secondary coating, pre-baking, sintering, and unloading;

[0038] The post-process includes the following steps:

[0039] Step 9: First coating: transfer the electroplated product to the coating line, set the epoxy resin JTF-1082 coating liquid, its viscosity is 20-24S, and the coating liquid temperature is ≤10℃. Through forward and reverse swing for 45 seconds each, the surface is coated with epoxy resin to increase the corrosion resistance of the product;

[0040] Step 10: Pre-baking and sintering. Place the products from step 9 evenly on the mesh belt, set the mesh belt pre-baking temperature to 100-150°C, pre-baking time to 20 minutes, sintering temperature to 210-220°C, sintering time to 20 minutes, and mesh belt speed to 24 cm / min, so that the coating can obtain better bonding strength;

[0041] Step 11: Second coating: After the first coating is sintered, the product is transferred to the coating line, and the epoxy resin JTF-1082 coating liquid is set, the viscosity of which is 20-24S, and the coating liquid temperature is ≤10℃. The epoxy resin coating on the surface is thickened by forward and reverse swaying for 45 seconds each, thereby increasing the corrosion resistance of the product;

[0042] Step 12: Pre-baking and sintering, place the products completed in step 11 evenly on the mesh belt, set the mesh belt pre-baking temperature to 100-150℃, pre-baking time to 20 minutes, sintering temperature to 210-220℃, sintering time to 20 minutes, and mesh belt speed to 24cm / min, so that the coating can obtain better bonding strength.

[0043] NT-111 is commercially available from Okuno Pharmaceutical Co., Ltd.

[0044] Embodiment 2: A coating method for high-strength fasteners, comprising a pre-process and a post-process,

[0045] The previous process includes cleaning, shot blasting, alkaline cyanide-free zinc plating, water washing, passivation, water washing, sealing, and drying;

[0046] The steps include:

[0047] Step 1: Cleaning, pre-treat the substrate, use the cavitation effect, acceleration effect and straight flow effect of ultrasonic waves in 60±5℃ liquid to directly and indirectly act on the liquid and dirt, so that the dirt layer is dispersed, emulsified and peeled off to achieve the purpose of cleaning, and then dry it in a mesh belt at 100-120℃;

[0048] Step 2: Shot blasting: steel shot with a diameter of 0.2mm and a hardness of HRC40-50 is accelerated through the shot blasting wheel to obtain higher kinetic energy, and then sprayed on the surface of the cleaned material for 18-25 minutes to generate impact and friction, clean up the surface oxide scale, rust, dirt and other impurities, improve the surface roughness, enhance the surface adhesion and corrosion resistance of the steel structure, and obtain the pre-treated substrate for standby use;

[0049] Step 3: Alkaline cyanide-free zinc plating, with a Zn2+ concentration of 10g / L, a NaOH concentration of 120g / L, and a ZN-111 solution with a 12ml / L additive. The pre-treated substrate is placed in the zinc plating tank of the electroplating line. The PLC controls the temperature at 15-35°C, the time at 70-110 minutes, and the current at 0.5-0.75A / dm2 before starting electrolysis to reduce the zinc ions on the metal surface to zinc metal, forming a dense zinc layer.

[0050] Step 4: Cleaning: the electroplating line is extracted and transferred to the cleaning tank. The cleaning tank is set for 3-5 seconds, the conductivity is ≤20μS / cm2, and it is cleaned 3 times to make the surface free of dirt;

[0051] Step 5: Passivation, the electroplating line is extracted and transferred to the passivation tank, the passivation solution has a pH value of 1.8-3.2, a temperature of 15-35°C, an A01-435D concentration of 60ml / L, and a Zn concentration of ≤10g / L, so that a chromate conversion film is formed on the surface of the zinc layer, reducing the chemical activity of zinc and obtaining better corrosion resistance.

[0052] Step 6: Cleaning: the electroplating line is automatically extracted and transferred to the cleaning tank. The cleaning tank is set for 3-5 seconds, the conductivity is ≤20μS / cm2, and it is cleaned 3 times to make the surface free of dirt;

[0053] Step 7: Sealing, the electroplating line is automatically extracted and transferred to the sealing tank, and the sealing agent ZBT-118 is used, the concentration is 100ml / L, the solution temperature is 35-50℃, and the soaking is 8-15S. A protective film is formed by sealing to prevent the metal ions in the electroplating solution from reacting with the surface of the electroplated object, thereby protecting the surface quality and appearance of the electroplated object and increasing the corrosion resistance of the product;

[0054] Step 8: Drying, adjust the parameters of the drying machine, time 10-15 minutes, temperature 70-100℃, speed 400-400 rpm;

[0055] The post-process includes coating, pre-baking, sintering, secondary coating, pre-baking, sintering, and unloading;

[0056] The post-process includes the following steps:

[0057] Step 9: First coating: transfer the electroplated product to the coating line, set the epoxy resin JTF-1082 coating liquid, its viscosity is 20-24S, and the coating liquid temperature is ≤10℃. Through forward and reverse swing for 45 seconds each, the surface is coated with epoxy resin to increase the corrosion resistance of the product;

[0058] Step 10: Pre-baking and sintering. Place the products from step 9 evenly on the mesh belt, set the mesh belt pre-baking temperature to 100-150°C, pre-baking time to 20 minutes, sintering temperature to 210-220°C, sintering time to 20 minutes, and mesh belt speed to 24 cm / min, so that the coating can obtain better bonding strength;

[0059] Step 11: Second coating: After the first coating is sintered, the product is transferred to the coating line, and the epoxy resin JTF-1082 coating liquid is set, the viscosity of which is 20-24S, and the coating liquid temperature is ≤10℃. The epoxy resin coating on the surface is thickened by forward and reverse swaying for 45 seconds each, thereby increasing the corrosion resistance of the product;

[0060] Step 12: Pre-baking and sintering, place the products completed in step 11 evenly on the mesh belt, set the mesh belt pre-baking temperature to 100-150℃, pre-baking time to 20 minutes, sintering temperature to 210-220℃, sintering time to 20 minutes, and mesh belt speed to 24cm / min, so that the coating can obtain better bonding strength.

[0061] NT-111 is commercially available from Okuno Pharmaceutical Co., Ltd.

[0062] Embodiment 3: A coating method for high-strength fasteners, comprising a pre-process and a post-process,

[0063] The previous process includes cleaning, shot blasting, alkaline cyanide-free zinc plating, water washing, passivation, water washing, sealing, and drying;

[0064] The steps include:

[0065] Step 1: Cleaning, pre-treat the substrate, use the cavitation effect, acceleration effect and straight flow effect of ultrasonic waves in 60±5℃ liquid to directly and indirectly act on the liquid and dirt, so that the dirt layer is dispersed, emulsified and peeled off to achieve the purpose of cleaning, and then dry it in a mesh belt at 100-120℃;

[0066] Step 2: Shot blasting: steel shot with a diameter of 0.2mm and a hardness of HRC40-50 is accelerated through the shot blasting wheel to obtain higher kinetic energy, and then sprayed on the surface of the cleaned material for 18-25 minutes to generate impact and friction, clean up the surface oxide scale, rust, dirt and other impurities, improve the surface roughness, enhance the surface adhesion and corrosion resistance of the steel structure, and obtain the pre-treated substrate for standby use;

[0067] Step 3: Alkaline cyanide-free zinc plating, with a Zn2+ concentration of 14g / L, a NaOH concentration of 140g / L, and a ZN-111 solution with a 15ml / L additive. The pre-treated substrate is placed in the zinc plating tank of the electroplating line. The PLC controls the temperature at 15-35°C, the time at 70-110 minutes, and the current at 0.5-0.75A / dm2 before starting electrolysis to reduce the zinc ions to zinc metal on the metal surface, forming a dense zinc layer.

[0068] Step 4: Cleaning: the electroplating line is extracted and transferred to the cleaning tank. The cleaning tank is set for 3-5 seconds, the conductivity is ≤20μS / cm2, and it is cleaned 3 times to make the surface free of dirt;

[0069] Step 5: Passivation, the electroplating line is extracted and transferred to the passivation tank, the passivation solution has a pH value of 1.8-3.2, a temperature of 15-35°C, an A01-435D concentration of 80ml / L, and a Zn concentration of ≤10g / L, so that a chromate conversion film is formed on the surface of the zinc layer, reducing the chemical activity of zinc and obtaining better corrosion resistance.

[0070] Step 6: Cleaning: the electroplating line is automatically extracted and transferred to the cleaning tank. The cleaning tank is set for 3-5 seconds, the conductivity is ≤20μS / cm2, and it is cleaned 3 times to make the surface free of dirt;

[0071] Step 7: Sealing, the electroplating line is automatically extracted and transferred to the sealing tank, and the sealing agent ZBT-118 is used, the concentration is 150ml / L, the solution temperature is 35-50℃, and the soaking is 8-15S. A protective film is formed by sealing to prevent the metal ions in the electroplating solution from reacting with the surface of the electroplated object, thereby protecting the surface quality and appearance of the electroplated object and increasing the corrosion resistance of the product;

[0072] Step 8: Drying, adjust the parameters of the drying machine, time 10-15 minutes, temperature 70-100℃, speed 400-400 rpm;

[0073] The post-process includes coating, pre-baking, sintering, secondary coating, pre-baking, sintering, and unloading;

[0074] The post-process includes the following steps:

[0075] Step 9: First coating: transfer the electroplated product to the coating line, set the epoxy resin JTF-1082 coating liquid, its viscosity is 20-24S, and the coating liquid temperature is ≤10℃. Through forward and reverse swing for 45 seconds each, the surface is coated with epoxy resin to increase the corrosion resistance of the product;

[0076] Step 10: Pre-baking and sintering. Place the products from step 9 evenly on the mesh belt, set the mesh belt pre-baking temperature to 100-150°C, pre-baking time to 20 minutes, sintering temperature to 210-220°C, sintering time to 20 minutes, and mesh belt speed to 24 cm / min, so that the coating can obtain better bonding strength;

[0077] Step 11: Second coating: After the first coating is sintered, the product is transferred to the coating line, and the epoxy resin JTF-1082 coating liquid is set, the viscosity of which is 20-24S, and the coating liquid temperature is ≤10℃. The epoxy resin coating on the surface is thickened by forward and reverse swaying for 45 seconds each, thereby increasing the corrosion resistance of the product;

[0078] Step 12: Pre-baking and sintering, place the products completed in step 11 evenly on the mesh belt, set the mesh belt pre-baking temperature to 100-150℃, pre-baking time to 20 minutes, sintering temperature to 210-220℃, sintering time to 20 minutes, and mesh belt speed to 24cm / min, so that the coating can obtain better bonding strength.

[0079] NT-111 is commercially available from Okuno Pharmaceutical Co., Ltd.

[0080] Neutral salt spray test:

[0081] The implementation standard of the salt spray test is: GB / T5267.1, the detection basis standard is GB / T 10125-2012, and the detection is carried out using a detection equipment named precision salt spray tester and numbered CA-24-001. The detection environment is temperature: 23°C, humidity: 41%, and the test samples 1-5 are ordinary commercially available high-strength fasteners and samples 6-10 are high-strength fasteners prepared using the process of this solution.

[0082] The test results are as follows:

[0083] Sample NSS test time result Sample NSS test time result Sample 1 120H qualified Sample 6 400H qualified Sample 2 120H Slight corrosion Sample 7 400H qualified Sample 3 120H qualified Sample 8 400H qualified Sample 4 120H qualified Sample 9 400H qualified Sample 5 120H Slight corrosion Sample 10 400H qualified

[0084] The new black zinc coated shoe product has no white rust in the NSS salt spray test time of 400H, which is significantly longer than the normal black zinc passivation salt spray time of 120H.

[0085] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, and they should be covered by the protection scope of the present invention.

Claims

1. A coating method for high-strength fasteners, characterized in that: Including pre-process and post-process, The previous process includes cleaning, shot blasting, alkaline cyanide-free zinc plating, water washing, passivation, water washing, sealing, and drying; The steps include: Step 1: Cleaning, pre-treat the substrate, use the cavitation effect, acceleration effect and straight flow effect of ultrasonic waves in 60±5℃ liquid to directly and indirectly act on the liquid and dirt, so that the dirt layer is dispersed, emulsified and peeled off to achieve the purpose of cleaning, and then dry it in a mesh belt at 100-120℃; Step 2: Shot blasting: steel shot with a diameter of 0.2mm and a hardness of HRC40-50 is accelerated through the shot blasting wheel to obtain higher kinetic energy, and then sprayed on the surface of the cleaned material for 18-25 minutes to generate impact and friction, clean up the surface oxide scale, rust, dirt and other impurities, improve the surface roughness, enhance the surface adhesion and corrosion resistance of the steel structure, and obtain the pre-treated substrate for standby use; Step 3: Alkaline cyanide-free zinc plating, with Zn 2+ The concentration is 6-14g / L, the NaOH concentration is 100-140g / L, the additive is a solution with a ZN-111 content of 8-15ml / L, the pre-treated substrate is placed in the galvanizing tank of the electroplating line, the PLC controls the temperature at 15-35℃, the time is 70-110 minutes, and the current is 0.5-0.75A / dm 2 Then electrolysis is started to reduce the zinc ions to zinc metal on the metal surface, forming a dense zinc layer; Step 4: Cleaning: the electroplating line is extracted and transferred to the cleaning tank. The cleaning tank is set for 3-5 seconds, the conductivity is ≤20μS / cm2, and it is cleaned 3 times to make the surface free of dirt; Step 5: Passivation, the electroplating line is extracted and transferred to the passivation tank, the passivation solution has a pH value of 1.8-3.2, a temperature of 15-35°C, an A01-435D concentration of 40-80ml / L, and a Zn concentration of ≤10g / L, so that a chromate conversion film is formed on the surface of the zinc layer, reducing the chemical activity of zinc and obtaining better corrosion resistance. Step 6: Cleaning: the electroplating line is automatically extracted and transferred to the cleaning tank. The cleaning tank is set for 3-5 seconds, the conductivity is ≤20μS / cm2, and it is cleaned 3 times to make the surface free of dirt; Step 7: Sealing, the electroplating line is automatically extracted and transferred to the sealing tank, and the sealing agent ZBT-118 is used, with a concentration of 50-150ml / L, a solution temperature of 35-50℃, and soaked for 8-15S. A protective film is formed by sealing to prevent the metal ions in the electroplating solution from reacting with the surface of the electroplated object, thereby protecting the surface quality and appearance of the electroplated object and increasing the corrosion resistance of the product; Step 8: Drying, adjust the parameters of the drying machine, time 10-15 minutes, temperature 70-100℃, speed 400-400 rpm; The post-process includes coating, pre-baking, sintering, secondary coating, pre-baking, sintering, and unloading; The post-process includes the following steps: Step 9: First coating: transfer the electroplated product to the coating line, set the epoxy resin JTF-1082 coating liquid, its viscosity is 20-24S, and the coating liquid temperature is ≤10℃. Through forward and reverse swing for 45 seconds each, the surface is coated with epoxy resin to increase the corrosion resistance of the product; Step 10: Pre-baking and sintering. Place the products from step 9 evenly on the mesh belt, set the mesh belt pre-baking temperature to 100-150°C, pre-baking time to 20 minutes, sintering temperature to 210-220°C, sintering time to 20 minutes, and mesh belt speed to 24 cm / min, so that the coating can obtain better bonding strength; Step 11: Second coating: After the first coating is sintered, the product is transferred to the coating line, and the epoxy resin JTF-1082 coating liquid is set, the viscosity of which is 20-24S, and the coating liquid temperature is ≤10℃. The epoxy resin coating on the surface is thickened by forward and reverse swaying for 45 seconds each, thereby increasing the corrosion resistance of the product; Step 12: Pre-baking and sintering, place the products completed in step 11 evenly on the mesh belt, set the mesh belt pre-baking temperature to 100-150℃, pre-baking time to 20 minutes, sintering temperature to 210-220℃, sintering time to 20 minutes, and mesh belt speed to 24cm / min, so that the coating can obtain better bonding strength.