Method for forming thermosetting coating on surface of hot-rolled strip steel and hot-rolled strip steel

Abstract

The invention discloses a method for forming a thermosetting coating on the surface of hot-rolled strip steel. The method comprises the steps that the hot-rolled strip steel is obtained; continuously monitoring the surface temperature of the hot-rolled strip steel; when the surface temperature reaches the set temperature, powder coating is sprayed to the surface of the hot-rolled strip steel; wherein the set temperature is determined based on the curing temperature of the powder coating; and cooling and curing the powder coating on the strip steel surface to form a film. The invention further discloses hot rolled strip steel, and the surface of the hot rolled strip steel is provided with the thermosetting coating prepared through the method. The coating is formed on the surface of the hot-rolled strip steel through waste heat of the hot-rolled strip steel, and the requirements for outer surface coating and inner surface coating-free corrosion prevention of the hot-rolled strip steel are met.

Description

Technical Field

[0001] The present invention relates to a steel material and a manufacturing method thereof, in particular to a hot-rolled steel strip and a method for forming a coating on the surface thereof. Background Art

[0002] Powder coating is a common coating currently available. Typically, it is applied by heating the target surface to melt and bond the coating powder, which is then cooled to form a continuous and dense coating.

[0003] Compared to traditional paints, powder coatings have a very high solids content and are solvent-free, eliminating the VOC emissions and environmental issues associated with traditional paints. Furthermore, their high solids content makes them more economical than traditional paints. Furthermore, their curing time is much shorter than traditional paints, leading to their widespread application.

[0004] However, since powder coatings require high-temperature heating to fuse into a film, the object often needs to be heated and kept warm for a certain period of time. Excessive energy consumption increases carbon emissions and becomes a major bottleneck restricting the development of this technology.

[0005] For example, a Chinese patent document with publication number CN103623978A, publication date March 21, 2014, and titled “A special production system for hot roll coating of steel pipes for corrosion protection and a special roll coating method using the special production system” discloses a special production system for hot roll coating of steel pipes for corrosion protection. The system can simultaneously roll coat the inside and outside of a steel pipe in one operation, thereby ensuring the integrity of the coating. Moreover, the coating thickness of the steel pipe after roll coating is uniform, which is easier to control than electrostatic spraying and dipping. The wall thickness of the molded part is uniform, and a coating of a desired thickness can be produced by simply changing the feed amount and adjusting the rotation speed of the steel pipe.

[0006] Another example is the Chinese patent document entitled "Pretreatment Method for Directly Coating on the Oxide Layer of a Hot-Rolled Workpiece," with publication number CN115652392A and publication date January 31, 2023. The document discloses a pretreatment method for directly coating on the oxide layer of a hot-rolled workpiece, comprising the steps of preparing a chemical treatment solution, immersing the workpiece in the chemical treatment solution, applying an electric current, and rinsing and drying. The pretreatment method for directly coating on the oxide layer of a hot-rolled workpiece of the present invention enables subsequent direct coating on the oxide layer of the workpiece, avoiding the need for sandblasting or shot blasting before coating. This effectively addresses the issue of large-scale peeling of the coating after a period of use and shortened coating service life after the oxide layer has been applied. Summary of the Invention

[0007] One of the purposes of the present invention is to provide a method for forming a thermosetting coating on the surface of a hot-rolled strip, which utilizes the waste heat of the hot-rolled strip to form a coating on the surface of the hot-rolled strip to meet the needs of coating the outer surface of the hot-rolled strip and coating-free anti-corrosion of the inner surface.

[0008] In order to achieve the above object, the present invention provides a method for forming a thermosetting coating on the surface of a hot-rolled steel strip, comprising the steps of:

[0009] Obtaining hot-rolled strip steel;

[0010] Continuously monitor the surface temperature of hot-rolled strip;

[0011] When the surface temperature reaches a set temperature, spraying the powder coating onto the surface of the hot-rolled steel strip; wherein the set temperature is determined based on the curing temperature of the powder coating;

[0012] The powder coating cools and solidifies to form a film on the surface of the strip.

[0013] Furthermore, in the method for forming a thermosetting coating on the surface of a hot-rolled strip described in the present invention, a pretreatment step is also included between the steps of obtaining the hot-rolled strip and continuously monitoring the surface temperature of the hot-rolled strip, and the pretreatment step includes removing dust and oxide particles on the surface of the hot-rolled strip by compressed air blowing or mechanical friction.

[0014] Furthermore, in the method for forming a thermosetting coating on the surface of a hot-rolled steel strip described in the present invention, in the step of continuously monitoring the surface temperature of the hot-rolled steel strip, an infrared thermometer is used to measure the surface temperature of the hot-rolled steel strip without contact.

[0015] Furthermore, in the method for forming a thermosetting coating on the surface of a hot-rolled steel strip according to the present invention, the set temperature is 0-30° C. lower than the upper limit of the curing temperature range of the powder coating.

[0016] Furthermore, in the method for forming a thermosetting coating on the surface of a hot-rolled steel strip described in the present invention, the powder coating is selected from at least one of the following: epoxy powder, polyurethane powder, polyester powder, acrylic powder, and epoxy polyester powder.

[0017] Furthermore, in the method for forming a thermosetting coating on the surface of a hot-rolled steel strip described in the present invention, in the step of spraying powder coating onto the surface of the hot-rolled steel strip, electrostatic powder spraying is used when double-sided spraying is performed on the hot-rolled steel strip.

[0018] In the present invention, electrostatic powder spraying can reduce powder loss and also reduce the impact on the environment.

[0019] Another object of the present invention is to provide a hot-rolled strip having a thermosetting coating of a certain thickness on its surface. The coating can provide surface protection for the product during transportation, storage, use and service, prevent surface corrosion, reduce user painting, and facilitate user use.

[0020] In order to achieve the above object, the present invention provides a hot-rolled steel strip, which is produced by the above-mentioned method of forming a thermosetting coating on the surface of a hot-rolled steel strip, wherein the surface of the hot-rolled steel strip has a thermosetting coating.

[0021] Furthermore, in the hot-rolled steel strip of the present invention, the thickness of the thermosetting coating is 10 to 300 microns.

[0022] Furthermore, in the hot-rolled steel strip of the present invention, the thickness of the thermosetting coating is 15 to 60 microns.

[0023] Furthermore, in the hot-rolled steel strip of the present invention, the thickness of the thermosetting coating is 20 to 40 microns.

[0024] The method for forming a thermosetting coating on the surface of a hot-rolled steel strip and the hot-rolled steel strip according to the present invention have the following advantages and beneficial effects compared to the prior art:

[0025] The hot-rolled steel strip and the thermosetting coating of the present invention are tightly bonded, and adhesion is better than level 1 in a 100-grid method or a prying method test. The rusting time of a coating of 60 microns and above in a salt spray test is greater than 240 hours, and the single-side corrosion width after 480 hours of salt spray testing after cross-scribing is less than 2 mm.

[0026] The thermosetting coating for hot-rolled steel strip described in this invention also meets certain deformation requirements. Most fundamentally, it can withstand surface cracking as the strip is coiled, allowing for a certain degree of bending without cracking, bulging, or peeling, as required by the user. Furthermore, for coatings less than 30 microns thick, 180-degree bending (with a bending radius of at least five times the thickness of the steel plate) is possible without noticeable peeling on the inner surface or visible cracking on the outer surface.

[0027] In addition, coating damage caused by welding, cutting or forming can be repaired by subsequent local coating of the same type of coating to avoid affecting the surface performance of the final product. The surface performance can also be further enhanced and the impact can be eliminated by applying a topcoat to the final component.

[0028] The hot-rolled steel strip of the present invention will not have black oxide scale particles fall off during normal transportation and indoor storage, and can be touched by human hands without pollution or residue.

[0029] The hot-rolled steel strip of the present invention has good corrosion resistance, wherein the pre-treatment coating can ensure that the surface of the steel strip is free of corrosion.

[0030] The hot-rolled steel strip of the present invention can reduce the user's painting operations, and due to the application of thermal curing technology, the online painting operation itself hardly generates harmful gas emissions, thereby greatly reducing environmental pollution.

[0031] The method of forming a thermosetting coating on the surface of a hot-rolled steel strip described in the present invention utilizes the waste heat of the hot-rolled steel strip itself to achieve the curing of the coating, thereby greatly saving energy consumption and being more low-carbon and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The interlayer structure of the hot-rolled steel strip having a thermosetting coating on its surface according to the present invention is schematically shown.

[0033] Figure 2 The figure schematically shows the implementation system diagram of the method for forming a thermosetting coating on the surface of a hot-rolled steel strip according to the present invention. DETAILED DESCRIPTION

[0034] The method for forming a thermosetting coating on the surface of a hot-rolled strip and the hot-rolled strip of the present invention will be further explained and illustrated below in conjunction with specific embodiments and drawings in the specification. However, such explanation and illustration do not constitute an undue limitation on the technical solution of the present invention.

[0035] Figure 1 The interlayer structure of the hot-rolled steel strip having a thermosetting coating on its surface according to the present invention is schematically shown.

[0036] like Figure 1 As shown, the hot rolled steel strip comprises a hot rolled base plate 1 and a thermosetting coating 2. Figure 1 As shown, in this embodiment, both the upper and lower surfaces of the hot-rolled substrate 1 are provided with thermosetting coatings 2 .

[0037] Of course, in other embodiments, the thermosetting coating 2 may be provided on only one surface of the hot-rolled substrate 1 .

[0038] In some embodiments, the thickness of the thermosetting coating can be 10 to 300 microns to meet different corrosion resistance and processing requirements.

[0039] For products that require laser cutting, the thickness of the thermosetting coating may be 15 to 60 microns. In some more preferred embodiments, the thickness of the thermosetting coating may be 20 to 40 microns.

[0040] Figure 2 The figure schematically shows the implementation system diagram of the method for forming a thermosetting coating on the surface of a hot-rolled steel strip according to the present invention.

[0041] In some embodiments, the method for forming a thermosetting coating on the surface of a hot-rolled steel strip according to the present invention can be implemented using the implementation system, which includes:

[0042] Uncoiling device A, welding device B, straightening device C, surface cleaning device D, powder spraying device E, auxiliary heating device F, cooling device G, surface inspection device H and temperature measuring device I.

[0043] In some embodiments, a hot rolled steel strip having a thermosetting coating on its surface is produced based on the following steps:

[0044] S1: Obtain a hot-rolled substrate based on the following steps:

[0045] Uncoiling, welding, and straightening: The hot-rolled strip to be processed is uncoiled using the uncoiling device A, welded together using the welding device B, and then sent to the straightening device C for straightening. The plate shape of the hot-rolled strip to be processed is optimized to ensure that the surface flatness of the hot-rolled strip meets the requirements of subsequent surface treatment operations.

[0046] S2: Pretreatment step: The surface cleaning device D is used to clean the dust and oxide particles on the surface of the straightened hot-rolled strip to ensure that the cleanliness of the hot-rolled strip surface meets the surface treatment requirements.

[0047] It should be noted that if there is no step to remove the oxide scale in the pretreatment process, sandblasting is required to remove the oxide scale generated in the front-end process before the strip enters the heat treatment. The oxide scale on the strip surface can be removed by sandblasting and other methods, and the formation of new oxide scale on the strip surface can be reduced or even prevented during the high-temperature heat treatment process by inert or reducing gas protection.

[0048] In some more specific embodiments, compressed air blowing may be used for surface cleaning, and the compressed air temperature and compressed air flow rate may be controlled to prevent the hot-rolled strip from losing temperature.

[0049] S3: Continuously monitor the surface temperature of the hot-rolled strip: A temperature measuring device I (e.g., an infrared thermometer) continuously and non-contactly measures the surface temperature of the hot-rolled strip. This surface temperature measurement covers the entire subsequent coating and curing process. This measured surface temperature information can be used to optimize the start and end times of material feeding and determine the hot-rolled strip speed, ensuring that the coating is fully welded and cured throughout the entire process, resulting in a continuous, dense, and consistent thermosetting coating that meets thickness and quality requirements.

[0050] S4: Powder spraying: When the surface temperature of the hot-rolled strip reaches a suitable temperature range, the powder spraying device E is started to apply powder coating to the surface of the hot-rolled strip.

[0051] In the present invention, prior to the powder coating step, it is necessary to confirm that the surface temperature of the hot-rolled steel strip is within the curing temperature range to ensure that the residual heat of the hot-rolled steel strip can complete the film-forming process while maintaining stable powder coating performance. In some embodiments, preliminary experiments can be conducted using hot-rolled steel plates of the same specifications to determine the curing temperature of the powder coating, and an appropriate temperature margin can be reserved to ensure that the powder coating can complete the film-forming process at this temperature margin to obtain a thermosetting coating.

[0052] In some more specific embodiments, the set temperature (ie, the feeding temperature for spraying the powder coating onto the surface of the hot-rolled steel strip) is 0-30° C. lower than the upper limit of the curing temperature range of the powder coating.

[0053] In the powder spraying step, the amount of powder coating to be added per unit time can be determined based on the area of ​​the hot-rolled strip to be coated per unit time (the real-time hot-rolled strip speed multiplied by the width of the hot-rolled strip) and the target thermosetting coating thickness, thereby controlling the coating delivery amount of each nozzle and ultimately achieving precise control of the coating film thickness on the surface of the hot-rolled strip at different speeds.

[0054] In some specific implementations, when double-sided spraying is performed on the hot-rolled steel strip, an electrostatic powder spraying process may be used; when single-sided spraying is performed on the hot-rolled steel strip, ordinary spraying may be used.

[0055] In some embodiments, the coating powder used for spraying is selected from at least one of the following: epoxy powder, polyurethane powder, polyester powder, acrylic powder, and epoxy polyester powder. The use of the above powders can ensure good adhesion to the oxide scale on the surface of the hot-rolled steel strip after high-temperature welding.

[0056] During the powder coating step, the surface temperature of the hot-rolled steel strip is continuously monitored by temperature measuring device I to ensure that the coating remains within the melting and curing temperature range for a sufficient period of time to fully complete the film-forming process. If the surface temperature of the steel strip is found to be lower than the lower limit of the thermosetting coating curing temperature range, the temperature is raised by auxiliary heating device F (hot air device, radiation device, infrared device, or induction heating device) to ensure that the powder coating completes the film-forming process.

[0057] S5: The powder coating cools and solidifies on the surface of the hot-rolled steel strip to form a film: After ensuring that the thermosetting coating is completely welded and formed into a film, the powder coating is cooled by a cooling device G (air cooling or water cooling). Of course, in some other embodiments, natural cooling can also be performed.

[0058] Avoid contact with the painted surface until the thermosetting coating has completely cured.

[0059] In some embodiments, before the thermosetting coating is 60% tack-cured, steps S2 to S5 may be repeated for multiple coatings to obtain a composite coating with stronger protective properties.

[0060] S6: Surface inspection: The surface inspection device H detects the curing degree, thickness, coverage and pinholes of the thermosetting coating on the upper and lower surfaces of the hot-rolled strip to ensure that the thermosetting coating is continuous, dense and has completed surface curing.

[0061] S7: Packaging and warehousing: When the delivery form is steel coil, the hot-rolled strip is trimmed and cut into strips longitudinally, and the part of the hot-rolled strip that fails the surface inspection is cut off, and the strip is re-coiled and coded, and packed for storage; when the delivery form is steel plate, the hot-rolled strip is trimmed, chamfered, and cut to length, and the part of the hot-rolled strip that fails the surface inspection is cut off, and the strip is cross-cut and stacked, and the strip is coded, packed and stored.

[0062] In order to verify the implementation effect of this case, the present invention sets preferred Examples 1-6, which all use BS960E as the hot-rolled substrate. Table 1 lists the specific process parameters of the method for forming a thermosetting coating on the surface of a hot-rolled strip used in Examples 1-6.

[0063] Table 1.

[0064]

[0065]

[0066] In order to verify the effects of each embodiment, the bonding performance test between the hot-rolled steel strip and the thermosetting coating and the corrosion resistance test of the thermosetting coating were conducted on each embodiment, and the test results are listed in Table 2, where:

[0067] (1) Test the adhesion of thermosetting coating using the 100-grid method;

[0068] (2) Salt spray test: using the standard ASTM B117.

[0069] Table 2.

[0070]

[0071]

[0072] As shown in Table 2, the thermosetting coatings of various embodiments of the present invention exhibited adhesion levels exceeding Class 1 using the 100-grid method. For coatings thicker than 60 microns, used as anti-corrosion primers or topcoats, the rust onset time in salt spray tests exceeded 240 hours, and the corrosion extension width after 480 hours of salt spray exposure after cross-scribing was less than 2 mm. Furthermore, coatings less than 30 microns thick could be bent 180 degrees (with a bending radius of at least five times the thickness of the steel plate) without noticeable peeling on the inner surface or visible cracking on the outer surface.

[0073] From Table 1 and Table 2, it can be seen that Examples 1, 4, 5, and 6 provide coating-free applications under various requirements, and sequentially provide corrosion resistance guarantees in environments ranging from mild to severe corrosion.

[0074] Among them, Example 6 adopts multi-layer coating, which is coated with epoxy primer powder coating and polyurethane topcoat powder coating. While obtaining better corrosion resistance, it also obtains better weather resistance, water resistance, wear resistance and appearance characteristics, and is suitable for heavy-duty anti-corrosion application scenarios that do not require painting.

[0075] Example 3 is a shop primer used mainly to address surface rust problems during production, storage and transportation. It achieves better processing performance with an extremely thin coating and has almost no effect on subsequent cutting, forming and painting.

[0076] Example 2 is for primer use, taking into account both corrosion resistance and processing performance. It provides high corrosion resistance and recoatability through the high adhesion of epoxy resin, while having minimal impact on subsequent cutting, forming and painting.

[0077] In actual use, these plates can be cut mechanically or by water jet, can be bent and deformed to a certain extent, can be connected by riveting, or can be bevel welded, but both sides of the weld need to be polished to avoid burning. After the connection is completed, they are repainted with epoxy paint and polyurethane topcoat.

[0078] It should be noted that the above embodiments are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith that can be directly derived from or easily associated with the contents disclosed by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A method for forming a thermosetting coating on the surface of a hot-rolled steel strip, characterized in that: Including steps: Obtaining hot-rolled strip steel; Continuously monitor the surface temperature of hot-rolled strip; When the surface temperature reaches a set temperature, spraying the powder coating onto the surface of the hot-rolled steel strip; wherein the set temperature is determined based on the curing temperature of the powder coating; The powder coating cools and solidifies to form a film on the surface of the strip.

2. The method for forming a thermosetting coating on the surface of a hot-rolled steel strip according to claim 1, wherein: A pretreatment step is included between the steps of obtaining the hot-rolled steel strip and continuously monitoring the surface temperature of the hot-rolled steel strip. The pretreatment step includes removing dust and oxide particles on the surface of the hot-rolled steel strip by means of compressed air blowing or mechanical friction.

3. The method for forming a thermosetting coating on the surface of a hot-rolled steel strip according to claim 1, wherein: In the step of continuously monitoring the surface temperature of the hot-rolled strip, an infrared thermometer is used to measure the surface temperature of the hot-rolled strip without contact.

4. The method for forming a thermosetting coating on the surface of a hot-rolled steel strip according to claim 1, wherein: The set temperature is 0-30° C. lower than the upper limit of the curing temperature range of the powder coating.

5. The method for forming a thermosetting coating on the surface of a hot-rolled steel strip according to claim 1, wherein: The powder coating is selected from at least one of the following: epoxy powder, polyurethane powder, polyester powder, acrylic powder, and epoxy polyester powder.

6. The method for forming a thermosetting coating on the surface of a hot-rolled steel strip according to claim 1, wherein: In the step of spraying the powder coating onto the surface of the hot-rolled steel strip, electrostatic powder spraying is adopted when double-sided spraying is performed on the hot-rolled steel strip.

7. A hot rolled steel strip, characterized in that: It is produced by the method according to any one of claims 1 to 6, and the surface of the hot-rolled steel strip has a thermosetting coating.

8. The hot rolled steel strip according to claim 7, wherein: The thickness of the thermosetting coating is 10 to 300 microns.

9. The hot rolled steel strip according to claim 8, wherein: The thickness of the thermosetting coating is 15 to 60 microns.

10. The hot rolled steel strip according to claim 9, wherein: The thickness of the thermosetting coating is 20 to 40 microns.

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