Anti-corrosion process for stainless steel door plate of refrigerated container

Abstract

The invention discloses an anti-corrosion process for a stainless steel door plate of a refrigerated container. The anti-corrosion process comprises the following steps: (1) pretreating the stainless steel door plate of the refrigerated container; (2) manufacturing a door plate unit, wherein the door plate unit comprises a connecting plate and two treated refrigerated container stainless steel door plates; (3) feeding the door panel unit into a powder spraying chamber, spraying powder to the door panel unit for the first time by adopting an electrostatic spraying gun, and feeding the door panel unit into a curing oven for curing after the first-time powder spraying is finished; (4) second-time powder spraying is conducted on the door plate unit, and the door plate unit is fed into the curing oven to be cured after second-time powder spraying is completed; and (5) after curing is completed, the door plate units are naturally cooled to the room temperature, buckling positioning is relieved, and the refrigerated container stainless steel door plate subjected to preservative treatment is obtained. Uniform anti-corrosion spraying of the refrigerated container stainless steel door plate can be achieved, the technological process is environmentally friendly, green and energy-saving, and the anti-corrosion performance of the refrigerated container stainless steel door plate can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of container corrosion prevention, in particular to a corrosion prevention process for a stainless steel door plate of a refrigerated container. BACKGROUND

[0002] As the core carrier of cold chain logistics, the door plate of a refrigerated container is exposed to a high-salt-mist and high-humidity environment during marine transportation for a long time, and needs to withstand high-temperature and low-temperature cycles under refrigeration working conditions, so it has very high requirements for corrosion resistance. At present, the door plate of a refrigerated container is mostly made of stainless steel, and the surface corrosion prevention process mainly includes traditional paint spraying and conventional electrostatic powder spraying.

[0003] The surface corrosion prevention process for the door plate of a refrigerated container currently has the following defects: first, the coating of the traditional paint spraying process has poor corrosion resistance, and the salt spray test can usually only last for a few hundred hours, which is difficult to meet the corrosion prevention requirements of long-term marine transportation of a refrigerated container. In addition, the paint contains volatile harmful substances, has poor environmental protection, and has low utilization rate of raw materials, which can easily cause waste of raw materials during production and has no effective recycling method. Second, when the conventional electrostatic powder spraying process is used to treat finished stainless steel door plates, the door plates need to be sanded in advance using brown corundum. A large amount of dust is generated during the sanding process of brown corundum, which not only pollutes the production environment, but also can harm the health of the operators. In addition, sanding operation produces high noise, which causes noise pollution to the surrounding environment, and the sanding process consumes additional energy to drive related equipment. Third, the existing surface roughening process for stainless steel door plates causes surface pollution due to the easy pulverization of brown corundum, resulting in insufficient adhesion between the coating and the substrate, and problems such as peeling and cracking after long-term use.

[0004] In addition, there is a lack of a special spraying positioning structure for the door plate of a refrigerated container in the prior art, which has low efficiency when processing in batches and is difficult to ensure product consistency.

[0005] Therefore, it is a technical problem to be solved in the field to develop a stainless steel door plate corrosion prevention process that takes into account corrosion resistance, uniformity of spraying, production efficiency, and environmental protection and energy saving. SUMMARY

[0006] The purpose of the present application is to provide a corrosion prevention process for a stainless steel door plate of a refrigerated container, which can achieve uniform corrosion prevention spraying for the stainless steel door plate of a refrigerated container, is environmentally friendly, energy-saving and green in the process, and can effectively improve the corrosion resistance of the stainless steel door plate of a refrigerated container.

[0007] To this end, the present application provides a corrosion prevention process for a stainless steel door plate of a refrigerated container, comprising: (1) sequentially performing degreasing, pickling, passivation, washing and drying treatment on the stainless steel door plate of a refrigerated container; (2) Fabricate door panel units, which include a connecting plate and two treated stainless steel door panels of refrigerated containers. The two treated stainless steel door panels of refrigerated containers are respectively attached to both sides of the connecting plate. (3) Send the door panel unit into the powder spraying chamber and use an electrostatic spray gun to spray the door panel unit for the first time. After the first powder spraying is completed, send the door panel unit into the curing oven for curing. (4) Apply a second powder coating to the door panel unit. After the second powder coating is completed, send the door panel unit into the curing oven for curing. (5) After curing, allow the door panel unit to cool naturally to room temperature, release the fastening and positioning, and obtain the anti-corrosion treated stainless steel door panel of the refrigerated container.

[0008] Preferably, in step (1), the surface roughness of the stainless steel door panel of the refrigerated container is Rz10-20μm.

[0009] Preferably, in step (1), an alkaline degreasing agent is used to degrease the stainless steel door panel of the refrigerated container to remove oil stains and metal debris adhering to the surface. The degreasing temperature is 40-60℃ and the degreasing time is 5-10 minutes.

[0010] Preferably, in step (1), pickling is performed using a pickling solution to clean the oxide scale and impurities in the roughening grooves on the surface of the stainless steel door panel of the refrigerated container; the pickling solution includes 5-10% nitric acid and 2-5% hydrofluoric acid by mass, the pickling temperature is 40-60℃, and the pickling time is 10-30min.

[0011] Preferably, in step (1), a 20-25% nitric acid solution is used for passivation treatment to form a dense Cr2O3 passivation film on the roughened surface; the passivation temperature is 60-70℃ and the passivation time is 30-60min.

[0012] Preferably, in step (1), after cleaning with deionized water, the stainless steel door panel of the refrigerated container is dried in a drying oven at 120-150℃ for 5-10 minutes to ensure that the surface of the stainless steel door panel is dry and free of residue.

[0013] Preferably, in steps (3) and (4), the powder spraying parameters are set as follows: electrostatic voltage is 60-80kV, compressed air pressure is 0.3-0.5MPa, distance from spray gun nozzle to door panel is 150-300mm, powder output is 400g / min, and conveyor chain speed is 4.5-5.5m / min.

[0014] Preferably, in step (3), the curing temperature of the first powder spraying is 100℃-150℃, the curing time is 1-10min, and the thickness of the first powder spraying is 35-45μm.

[0015] Preferably, in step (4), the curing temperature of the second powder spraying is 160℃-180℃, the curing time is 5-15min, and the thickness of the second powder spraying is 45-55μm.

[0016] Compared with the prior art, the advantages and positive effects of the present invention are: Excellent corrosion resistance: The pretreatment process is designed specifically for the roughened surface characteristics of finished stainless steel after roughening treatment. It can not only clean impurities in the roughening grooves, but also form a uniform passivation film on the roughened surface. This film forms a dual effect of mechanical interlocking and chemical bonding with the electrostatic powder coating, which significantly improves the coating adhesion. The salt spray resistance can reach more than 1200 hours, which is more corrosion resistant than traditional paint coatings and is suitable for the harsh environment of refrigerated container marine transportation.

[0017] Excellent coating uniformity: The innovative snap-fit ​​positioning method not only solves the problem of shaking when spraying large stainless steel door panels, but also forms a uniform spraying channel through the spacing design, effectively eliminating spraying dead corners, ensuring that the coating thickness on the surface and edges of the door panel is consistent, and avoiding defects such as exposed substrate and drips.

[0018] High production efficiency: Each set of interlocking units can process 2 door panels at the same time, and the batch spraying efficiency is more than 50% higher than that of conventional processes; the positioning fixtures can be reused, reducing production auxiliary costs and making them suitable for large-scale production.

[0019] Environmentally friendly and cost-controllable: It adopts environmentally friendly powder coating, with no volatile harmful substances emitted, meeting the requirements of green production; the powder utilization rate exceeds 90%, reducing material loss by 30% compared with traditional spraying process, and can significantly reduce maintenance costs in the long term.

[0020] Significant green and energy-saving effects: This process uses roughened stainless steel plates as raw materials, eliminating the need for brown corundum sandblasting and completely preventing dust and noise pollution generated during sandblasting, thus improving the production environment and protecting the health of operators. It also eliminates the energy consumption of sandblasting equipment, reducing overall energy consumption. Furthermore, the powder used in the powder coating process has excellent recyclability; unattached powder can be recycled and reused, significantly reducing raw material waste. Compared to traditional painting processes, this not only reduces raw material costs but also decreases waste emissions and environmental pollution. Moreover, the powder coating equipment consumes less energy, further reducing energy consumption and aligning with current environmental protection and energy-saving industrial policies and development trends.

[0021] Other features and advantages of the present invention will become clearer after reading the detailed embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0022] Figure 1 This is one of the structural schematic diagrams of an embodiment of the door panel unit of the present invention; Figure 2 yes Figure 1 Enlarged view of section A in the middle; Figure 3 This is a second structural schematic diagram of an embodiment of the door panel unit of the present invention; Figure 4 This is the third structural schematic diagram of an embodiment of the door panel unit of the present invention;

[0023] Connecting plate 10, bonding plate 11, spring steel ball buckle 12, hook 13; Refrigerated container stainless steel door panel 20, overlapping panel 21, buckle through hole 22. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] This invention discloses an anti-corrosion process for stainless steel door panels of refrigerated containers, comprising the following steps: (1) The stainless steel door panels of the refrigerated container are subjected to degreasing, pickling, passivation, water washing and drying in sequence; The surface roughness of stainless steel door panels for refrigerated containers is Rz10-20μm.

[0026] Degreasing is performed using an alkaline degreasing agent to remove oil stains and metal debris adhering to the surface of the stainless steel door panels of refrigerated containers. The degreasing temperature is 40-60℃ and the degreasing time is 5-10 minutes.

[0027] Pickling is performed using a pickling solution to remove oxide scale and impurities from the roughened grooves on the surface of the stainless steel door panels of refrigerated containers. The pickling solution consists of 5-10% nitric acid and 2-5% hydrofluoric acid by mass, with a pickling temperature of 40-60℃ and a pickling time of 10-30 minutes.

[0028] A 20-25% nitric acid solution was used for passivation treatment to form a dense Cr2O3 passivation film on the roughened surface; the passivation temperature was 60-70℃ and the passivation time was 30-60 min.

[0029] After being cleaned with deionized water, the stainless steel door panels of the refrigerated container are dried in a drying oven at 120-150℃ for 5-10 minutes to ensure that the surface of the stainless steel door panels is dry and free of residue.

[0030] (2) Fabricate door panel unit, which includes connecting plate 10 and two processed stainless steel door panels 20 of refrigerated container, and the two processed stainless steel door panels 20 are respectively attached to both sides of connecting plate 10. The connecting plate 10 has a symmetrical structure. The two corresponding sides of the connecting plate 10 are respectively fixed with a bonding plate 11. The bonding plate 11 is rectangular, and the side length of the bonding plate 11 is equal to the side length of the stainless steel door panel 20 of the refrigerated container. The stainless steel door panel 20 of the refrigerated container is bonded to the bonding plate 11.

[0031] The top of the bonding plate 11 is connected to a spring steel ball buckle 12, and the top of the stainless steel door panel 20 of the refrigerated container is vertically fixed with an overlapping plate 21. The overlapping plate 21 is provided with a buckle through hole 22. The overlapping plate 21 overlaps the top of the bonding plate 11, and the spring steel ball of the spring steel ball buckle 12 is engaged in the buckle through hole 22, so that the stainless steel door panel 20 of the refrigerated container can be engaged and connected to the bonding plate 11.

[0032] The diameter of the snap-fit ​​through hole 22 is smaller than the diameter of the spring ball, and slightly larger than the maximum exposed diameter of the spring ball, so as to ensure that the stainless steel door panel 20 of the refrigerated container is snapped and connected to the bonding plate 11.

[0033] The spring ball buckle 12 is a common spring ball buckle in this technical field, and no specific limitation is made here.

[0034] The top of the connecting plate 10 is provided with a hook 13, which can be used to attach the door panel unit to the power chain, so that the door panel unit can move in a straight line, thereby facilitating the entry and exit of the door panel unit into the powder spraying chamber.

[0035] (3) Send the door panel unit into the powder spraying chamber and use an electrostatic spray gun to spray the door panel unit for the first time. After the first powder spraying is completed, send the door panel unit into the curing oven for curing. The curing temperature for the first powder coating is 100℃-150℃, the curing time is 1-10 min, and the thickness of the first powder coating is 35-45 μm.

[0036] (4) Apply a second powder coating to the door panel unit. After the second powder coating is completed, send the door panel unit into the curing oven for curing. The curing temperature for the second powder spraying is 160℃-180℃, the curing time is 5-15min, and the thickness of the second powder spraying is 45-55μm.

[0037] In steps (3) and (4), the powder spraying parameters are set as follows: electrostatic voltage is 60-80kV, compressed air pressure is 0.3-0.5MPa, distance from spray gun nozzle to door panel is 150-300mm, powder output is 400g / min, and conveyor chain speed is 4.5-5.5m / min.

[0038] In steps (3) and (4), the powder coating includes at least one of resin, curing agent, pigment, filler, additive, matting agent and light stabilizer. The mass fraction of the resin is 48%-58%, the mass fraction of the curing agent is 4%-6%, the mass fraction of the pigment is 6%-12%, the mass fraction of the filler is 22%-32%, and the mass fraction of the light stabilizer is 2%-4%.

[0039] The resin includes saturated polyester resin, which has a hydroxyl value of 30-60 mg KOH / g and an acid value of 10-20 mg KOH / g. Saturated polyester resin has excellent weather resistance, gloss and color retention, and strong impact resistance after crosslinking with curing agent.

[0040] The curing agents include triglycidyl isocyanurate (TGIC) and / or hydroxyalkylamide (HAA). Triglycidyl isocyanurate (TGIC) has high curing efficiency and good salt spray resistance; hydroxyalkylamide (HAA) is an environmentally friendly curing agent and is non-toxic.

[0041] Pigments include weather-resistant pigments and / or rust-preventive pigments. Weather-resistant pigments include rutile titanium dioxide, phthalocyanine blue / green, and inorganic iron oxide pigments. Rust-preventive pigments can be zinc powder. Rutile titanium dioxide is UV resistant, zinc powder is a sacrificial anode for rust prevention, and phthalocyanine pigments have a weather resistance of >5 years.

[0042] The filler may include ultrafine barium sulfate and / or mica powder. Mica powder enhances the coating's water resistance and impermeability, while barium sulfate increases hardness.

[0043] The additives can be polyester-modified acrylates, and the matting agent can be fumed silica. The matting agent can adjust the gloss of the paint film (semi-gloss is commonly used for containers).

[0044] Light stabilizers can be hindered amines (HALS), which improve the outdoor weather resistance of containers.

[0045] (5) After curing, allow the door panel unit to cool naturally to room temperature, release the fastening and positioning, and obtain the anti-corrosion treated stainless steel door panel of the refrigerated container. Example

[0046] The anti-corrosion process for the stainless steel door panel of the refrigerated container in this embodiment includes the following steps: (1) Pretreatment: Select stainless steel roughened door panels of refrigerated containers with specifications of 2490mm×1074mm×1.6mm and mechanical roughening treatment, with a surface roughness Ra of 10μm; firstly, immerse the stainless steel roughened door panels of refrigerated containers in TL-30 alkaline degreasing agent at 45℃ for 8min to remove oil stains and metal debris from the surface of the stainless steel roughened door panels of refrigerated containers; then, immerse them in a mixture of 8% nitric acid and 3% hydrofluoric acid at 50℃ for 20min to clean the oxide scale and impurities in the roughening grooves of the stainless steel roughened door panels of refrigerated containers; then, immerse them in a 22% nitric acid solution at 65℃ for 45min to passivate and form a dense Cr2O3 passivation film on the roughened surface of the stainless steel roughened door panels of refrigerated containers; then, wash them with room temperature deionized water for 3min, and finally immerse them in a drying oven at 130℃ for 8min to dry, remove them and cool them to room temperature to obtain the pretreated stainless steel roughened door panels of refrigerated containers.

[0047] In this embodiment, since roughened stainless steel plate is used, there is no need to perform brown corundum sandblasting, which avoids dust and noise pollution generated by sandblasting, and saves the power consumption required for sandblasting equipment. According to calculations, compared with the traditional process that requires sandblasting, this step can reduce production energy consumption by about 15%-20%.

[0048] (2) The two pre-treated stainless steel door panels 20 of the refrigerated containers are installed on the connecting plate 10 to form a door panel unit.

[0049] (3) Send the door panel unit into the powder spraying chamber and use an electrostatic spray gun to spray the door panel unit for the first time. After the first powder spraying is completed, send the door panel unit into the curing oven for curing. During the curing process, maintain the hot air circulation speed in the oven at 0.8 m / s to ensure uniform temperature.

[0050] The curing temperature for the first powder coating is 120℃, the curing time is 5 minutes, and the thickness of the first powder coating is 40μm.

[0051] (4) Apply powder coating to the door panel unit for the second time. After the second powder coating is completed, send the door panel unit into the curing oven for curing. During the curing process, maintain the hot air circulation speed in the oven at 0.8 m / s to ensure uniform temperature.

[0052] The curing temperature for the second powder spraying is 160℃-180℃, the curing time is 10min, and the thickness of the second powder spraying is 50μm.

[0053] In steps (3) and (4), the electrostatic voltage is set to 70kV, the compressed air pressure to 0.4MPa, the distance from the spray gun nozzle to the door panel to be 200mm, the powder output to be 400g / min, and the conveyor chain speed to be 5m / min; low-temperature semi-crystalline powder is selected for all-round spraying, and the coating thickness is controlled at 90-110μm.

[0054] The powder coating booth is equipped with a high-efficiency powder recovery device. Powder that does not adhere to the door panel is recovered, screened, and reused. In this embodiment, the total powder utilization rate reaches over 92%, which significantly reduces raw material waste compared to the 30%-50% raw material utilization rate of traditional painting processes, while also reducing waste emissions. Furthermore, the electrostatic powder coating machine used in this embodiment has approximately 25% lower power than traditional paint spraying equipment, further reducing production energy consumption.

[0055] (5) Post-processing: After natural cooling to room temperature, disassemble the tooling and release the fasteners; use a coating thickness gauge to check the thickness of each part of the stainless steel door panel of the refrigerated container to ensure that the thickness deviation is ≤5μm, so as to obtain qualified stainless steel door panels of the refrigerated container that have undergone anti-corrosion treatment.

[0056] The quality of the passivation film was tested. Salt spray tests were conducted on the stainless steel door panels of refrigerated containers. The panels were continuously tested for 1200 hours in a 5% NaCl solution at 35°C. No rust spots were found on the surface of the stainless steel roughened door panels of the refrigerated containers, which met the anti-corrosion requirements. The salt spray resistance of the stainless steel door panels of refrigerated containers was ≥1200 hours.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. A corrosion-resistant process for stainless steel door panels of refrigerated containers, characterized in that, include: (1) The stainless steel door panels of the refrigerated container are subjected to degreasing, pickling, passivation, water washing and drying in sequence; (2) Fabricate door panel units, which include a connecting plate and two treated stainless steel door panels of refrigerated containers. The two treated stainless steel door panels of refrigerated containers are respectively attached to both sides of the connecting plate. (3) Send the door panel unit into the powder spraying chamber and use an electrostatic spray gun to spray the door panel unit for the first time. After the first powder spraying is completed, send the door panel unit into the curing oven for curing. (4) Apply a second powder coating to the door panel unit. After the second powder coating is completed, send the door panel unit into the curing oven for curing. (5) After curing, allow the door panel unit to cool naturally to room temperature, release the fastening and positioning, and obtain the anti-corrosion treated stainless steel door panel of the refrigerated container.

2. The anti-corrosion process for stainless steel door panels of refrigerated containers as described in claim 1, characterized in that, In step (1), the surface roughness of the stainless steel door panel of the refrigerated container is Rz10-20μm.

3. The anti-corrosion process for stainless steel door panels of refrigerated containers as described in claim 1, characterized in that, In step (1), an alkaline degreasing agent is used to degrease the stainless steel door panel of the refrigerated container to remove oil stains and metal debris. The degreasing temperature is 40-60℃ and the degreasing time is 5-10 minutes.

4. The anti-corrosion process for stainless steel door panels of refrigerated containers as described in claim 1, characterized in that, In step (1), pickling is performed using a pickling solution to clean the oxide scale and impurities in the roughening grooves on the surface of the stainless steel door panel of the refrigerated container. The pickling solution includes nitric acid with a mass fraction of 5-10% and hydrofluoric acid with a mass fraction of 2-5%, the pickling temperature is 40-60℃, and the pickling time is 10-30min.

5. The anti-corrosion process for stainless steel door panels of refrigerated containers as described in claim 1, characterized in that, In step (1), a 20-25% nitric acid solution is used for passivation treatment to form a dense Cr2O3 passivation film on the roughened surface; the passivation temperature is 60-70℃ and the passivation time is 30-60min.

6. The anti-corrosion process for stainless steel door panels of refrigerated containers as described in claim 1, characterized in that, In step (1), after cleaning with deionized water, the stainless steel door panel of the refrigerated container is dried in a drying oven at 120-150℃ for 5-10 minutes to ensure that the surface of the stainless steel door panel is dry and free of residue.

7. The anti-corrosion process for stainless steel door panels of refrigerated containers as described in claim 1, characterized in that, In steps (3) and (4), the powder spraying parameters are set as follows: electrostatic voltage is 60-80kV, compressed air pressure is 0.3-0.5MPa, distance from spray gun nozzle to door panel is 150-300mm, powder output is 400g / min, and conveyor chain speed is 4.5-5.5m / min.

8. The anti-corrosion process for stainless steel door panels of refrigerated containers as described in claim 1, characterized in that, In step (3), the curing temperature of the first powder spraying is 100℃-150℃, the curing time is 1-10min, and the thickness of the first powder spraying is 35-45μm.

9. The anti-corrosion process for stainless steel door panels of refrigerated containers as described in claim 1, characterized in that, In step (4), the curing temperature of the second powder spraying is 160℃-180℃, the curing time is 5-15min, and the thickness of the second powder spraying is 45-55μm.

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