Quality improving device and method for transverse fine line of zinc-aluminum-magnesium thin coated steel plate

Abstract

The invention discloses a device and a method for improving the quality of a transverse fine line of a zinc-aluminum-magnesium thin coated steel plate. The device comprises an air knife and an air knife nitrogen heating device, the method comprises the following steps: (1) degreasing and cleaning cold-rolled strip steel; (2) the cold-rolled strip steel is subjected to continuous annealing and hot dipping; (3) carrying out post-plating air knife purging on the plated strip steel by using a zinc-aluminum-magnesium thin-plated steel plate transverse fine line quality improving device; and 4) a subsequent process of plating the strip steel. The method is used for producing the zinc-aluminum-magnesium coated steel plate, the defects of transverse fine lines, clouds and the like of the coating are eliminated through the methods of reasonably adjusting the components of the plating solution, increasing the nitrogen heating function of the air knife and the like, and the method can be used for producing the hot-dip galvanized aluminum-magnesium coated steel plate with good appearance quality; the method has good industrial application value.

Description

Technical Field

[0001] This invention relates to a method for producing hot-dip galvanized aluminum-magnesium coated steel sheets with good appearance quality, and particularly to a device and method for improving the quality of transverse fine lines on thin zinc-aluminum-magnesium coated steel sheets. Background Technology

[0002] Zinc-aluminum-magnesium (ZAM) coated steel sheets are increasingly widely used due to their excellent corrosion resistance. Their extensive use as uncoated exterior parts makes the quality control of the coating's appearance crucial. However, the rich and complex phase structure of the ZAM coating itself presents several challenges for quality control. In particular, when the Mg content of the coating is ≥2%, the oxidation resistance of the plating solution decreases significantly. During the flow of the plating solution under the air knife, oxidation and slag formation are highly likely. The pinning effect of the zinc slag disrupts the smooth flow of the plating solution, resulting in defects such as transverse fine lines. This phenomenon is more pronounced when the single-sided coating thickness is ≤50g / m², due to the high air knife pressure, leading to surface quality abnormalities such as transverse fine lines and cloud-like appearance on the strip steel.

[0003] Previous studies generally agree that the formation of transverse fine lines and cloud-like appearance on the coating surface is due to the enrichment of the Zn phase. The height difference at the defect location is small, and the coating cools and solidifies instantly when the air knife blows through the strip steel surface, forming fine lines. This can be addressed by adjusting the air knife parameters. To improve the edge coating quality of thin zinc-aluminum-magnesium coatings, many steel manufacturers have invested considerable effort in experimentation and exploration.

[0004] Several authorized patents (such as CN201810462422.9, CN201310282928.9, CN202320350621.7, CN201621234388.2, and CN201921078928.6) have attempted to overcome the defects of color difference on the coating surface by adding trace elements to the plating solution and adding a nitrogen protective cover to the air knife purging area, thus achieving the effect of improving the appearance quality of zinc-aluminum-magnesium coatings and improving the solidification structure of zinc alloys. However, the above methods lack effective improvement measures for problems such as transverse fine lines in the coating.

[0005] However, in the face of actual production environments, improving the oxidation resistance of plating solutions and reducing defects such as transverse fine lines and cloudiness in the plating layer remains a challenge. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a device and method for improving the quality of transverse fine lines in zinc-aluminum-magnesium thin-coated steel plates.

[0007] This invention addresses the problem of defects such as transverse fine lines and cloudiness in current zinc-aluminum-magnesium coatings that affect the appearance quality of products. It proposes a method and apparatus for optimizing the composition of the plating solution and improving the leveling ability of the air knife purging process, thereby eliminating defects such as transverse fine lines and cloudiness in zinc-aluminum-magnesium coatings.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A device for improving the quality of transverse fine lines in zinc-aluminum-magnesium thin-coated steel plates, the device comprising an air knife and an air knife nitrogen heating device, the air knife nitrogen heating device being located on the outlet side of a booster fan; the air knife nitrogen heating device and the subsequent pipeline are equipped with a heat preservation device; the air knife cavity is equipped with a gas temperature measuring device, and the gas heating temperature is precisely controlled through closed-loop feedback control.

[0009] Furthermore, the gas temperature control range of the gas knife nitrogen heating device is 80-200℃, and the temperature control accuracy is ±2℃.

[0010] Furthermore, the distance between the nitrogen heating device for the air knife and the air knife cavity is ≤3m.

[0011] This invention also discloses a method for improving the quality of transverse fine lines on zinc-aluminum-magnesium thin-coated steel sheets, the method comprising the following steps: Step 1) Degrease and clean the cold-rolled strip steel; Step 2) The cold-rolled strip steel undergoes continuous annealing and hot-dip galvanizing; Step 3) Use the zinc-aluminum-magnesium thin-coated steel sheet transverse fine line quality improvement device to perform post-coating air knife blowing on the coated steel strip; Step 4) Subsequent processes for plating the steel strip.

[0012] Furthermore, in step 1), residual rolling oil, iron powder and non-metallic solid particles on the surface of the strip are removed by chemical degreasing and electrolytic degreasing. After the strip exits the degreasing tank, it is squeezed dry by the squeezing roller, then the degreasing liquid is washed and rinsed clean with hot water, and then dried by hot air.

[0013] Further, in step 2), after the strip steel is fully annealed in a N2 and H2 mixed atmosphere, it is immersed in a zinc pot. The immersion time of the strip steel in the plating solution is 1-10 seconds. The chemical composition of the plating solution is as follows (mass percentage): Al content 1-30.0%, Mg content 1-10.0%, Si content 0-2.0%. The plating solution also contains one or more of the following: Ca: 0.01-0.5%, Sr: 0.01-0.5%, B: 0-0.05%, Cr: 0-0.3%, Ti: 0.001-0.3%, Ni: 0.001-1.0%, Fe: 0.01-2.0%, with the balance being Zn and other unavoidable impurities.

[0014] Furthermore, in step 2), the temperature of the zinc pot is controlled at 390-550°C, based on the melting point of the actual plating solution composition plus 20-50°C, and the temperature of the strip steel entering the zinc pot is controlled at 400-550°C.

[0015] Furthermore, in step 3), the strip enters the air knife area. The air source for the air knife is N2 or other inert gas with a purity greater than 99%. The air knife pressure is controlled at 50–900 mbar, the air knife distance is 7–20 mm, the air knife height is 60–600 mm, the air knife angle is 0–-3°, and the gap between the air knife baffle and the strip is 2–8 mm.

[0016] Further, in step 4), after the air knife exits, the strip enters the post-plating cooling air box, where the cooling rate is 10-50℃ / s, and the strip temperature is <280℃ before entering the top roller; after passing the top roller, the strip enters the post-plating cooling downward section, passes through the cooling fan, and the strip temperature is <100℃. It then enters the quenching water tank for cooling, and is subsequently leveled, coated with a post-treatment film by a roller coater, dried, and then coiled.

[0017] The beneficial effects of this invention are: This invention is used in the production of zinc-aluminum-magnesium coated steel sheets. By rationally adjusting the composition of the plating solution and adding nitrogen heating function of the air knife, defects such as transverse fine lines and cloudiness in the coating are eliminated. It can be used to produce hot-dip galvanized aluminum-magnesium coated steel sheets with good appearance quality. This invention has good industrial application value. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the air knife nitrogen heating device of the present invention; The labels in the diagram are as follows: 1-Manual butterfly valve, 2-Electric butterfly valve, 3-Pipeline, 4-Booster fan, 5-Expansion joint, 6-Nitrogen heating device, 7-Vent valve, 8-Air knife. Detailed Implementation

[0019] The invention will be further described in detail below with reference to embodiments, such as the air knife nitrogen heating device of the zinc-aluminum-magnesium thin-coated steel plate transverse fine wire quality improvement device. Figure 1 As shown.

[0020] Example 1: Strip thickness 1.8mm, zinc coating weight 100g / m 2 The strip speed was 78 mpm, the air knife distance was 8 mm, the air knife pressure was 80 mbar, and the air knife height was 120 mm. Nitrogen gas was introduced for heating at 180℃. The aluminum content of the plating bath was 6.5%. The coating had no transverse fine lines and no cloudiness.

[0021] In contrast, Comparative Example 1: steel strip thickness 1.8mm, zinc coating weight 100g / m 2The strip speed was 78 mpm, the air knife distance was 8 mm, the air knife pressure was 57 mbar, and the air knife height was 120 mm. Nitrogen heating was not used. The aluminum content of the plating bath was 6.0%. The transverse fine lines and cloud-like appearance of the plating layer were quite noticeable.

[0022] Example 2: Strip thickness 1.8mm, zinc coating weight 100g / m 2 The strip speed was 78 mpm, the air knife distance was 8 mm, the air knife pressure was 75 mbar, and the air knife height was 120 mm. Nitrogen gas was introduced for heating at 150℃. The aluminum content of the plating solution was 6.5%. The coating had no transverse fine lines and no cloudiness.

[0023] In contrast, Comparative Example 2: strip thickness 1.8mm, zinc coating weight 120g / m 2 The air knife distance was 8mm, the air knife pressure was 54mbar, and the air knife height was 120mm. Nitrogen heating was not used. The aluminum content of the plating bath was 6.0%. Both fine transverse lines and a cloudy appearance were present in the plating layer, but were relatively minor.

[0024] Example 3: Strip thickness 2.0 mm, zinc coating weight 100 g / m 2 The strip speed was 73 mpm, the air knife distance was 8 mm, the air knife pressure was 69 mbar, and the air knife height was 120 mm. Nitrogen gas was introduced for heating at 120℃. The aluminum content of the plating solution was 6.5%. The coating had no transverse fine lines and no cloudiness.

[0025] In contrast, Comparative Example 3: strip thickness 2.0mm, zinc coating weight 100g / m 2 The strip speed was 73 MPa, the air knife distance was 8 mm, the air knife pressure was 53 mbar, and the air knife height was 120 mm. Without nitrogen heating, the transverse fine lines and cloud-like appearance of the coating were quite noticeable.

[0026] Example 8: Strip thickness 2.5mm, zinc coating weight 100g / m 2 The strip speed was 60 mpm, the air knife distance was 10 mm, the air knife pressure was 58 mbar, and the air knife height was 120 mm. Nitrogen gas was introduced for heating at 120℃. The aluminum content of the plating solution was 6.0%. The coating had no transverse fine lines or cloud-like defects.

[0027] In contrast, Comparative Example 4: strip thickness 2.5mm, zinc coating weight 120g / m 2 The strip speed was 60 mpm, the air knife distance was 10 mm, the air knife pressure was 48 mbar, and the air knife height was 120 mm. Nitrogen heating was not used. The aluminum content of the plating bath was 6.0%, and the transverse fine lines and cloud-like appearance of the coating were quite noticeable.

[0028] The specific parameters of the embodiments and comparative examples are shown in Table 1.

[0029] Table 1. Specific parameters of the examples and comparative examples

[0030] The above content is only used to illustrate the technical solution of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A device for improving the quality of transverse fine lines in zinc-aluminum-magnesium thin-coated steel sheets, the device comprising an air knife and an air knife nitrogen heating device, characterized in that: The air knife nitrogen heating device is located on the outlet side of the booster fan; the air knife nitrogen heating device and the pipeline thereafter are equipped with heat preservation devices; the air knife cavity is equipped with a gas temperature measuring device, and the gas heating temperature is precisely controlled through closed-loop feedback control.

2. The device for improving the quality of transverse fine lines in zinc-aluminum-magnesium thin-coated steel plates according to claim 1, characterized in that: The gas temperature control range of the gas knife nitrogen heating device is 80-200℃, and the temperature control accuracy is ±2℃.

3. The device for improving the quality of transverse fine lines in zinc-aluminum-magnesium thin-coated steel plates according to claim 1, characterized in that: The distance between the nitrogen heating device for the air knife and the air knife cavity is ≤3m.

4. A method for improving the quality of transverse fine lines on zinc-aluminum-magnesium thin-coated steel sheets, characterized in that: The method includes the following steps: Step 1) Degrease and clean the cold-rolled strip steel; Step 2) The cold-rolled strip steel undergoes continuous annealing and hot-dip galvanizing; Step 3) Use the zinc-aluminum-magnesium thin-coated steel sheet transverse fine line quality improvement device as described in claim 1 to perform post-coating air knife blowing on the coated steel strip; Step 4) Subsequent processes for plating the steel strip.

5. The method for improving the quality of transverse fine lines in zinc-aluminum-magnesium thin-coated steel sheets according to claim 4, characterized in that: In step 1), residual rolling oil, iron powder and non-metallic solid particles on the surface of the strip are removed by chemical degreasing and electrolytic degreasing. After the strip exits the degreasing tank, it is squeezed dry by the squeezing roller, then the degreasing liquid is washed and rinsed clean with hot water, and then dried by hot air.

6. The method for improving the quality of transverse fine lines in zinc-aluminum-magnesium thin-coated steel sheets according to claim 4, characterized in that: In step 2), the strip steel is fully annealed in a N2 and H2 mixed atmosphere and then immersed in a zinc pot. The immersion time of the strip steel in the plating solution is 1 to 10 seconds. The chemical composition of the plating solution is as follows (mass percentage): Al content 1 to 30.0%, Mg content 1 to 10.0%, Si content 0 to 2.0%. The plating solution also contains one or more of the following: Ca: 0.01 to 0.5%, Sr: 0.01 to 0.5%, B: 0 to 0.05%, Cr: 0 to 0.3%, Ti: 0.001 to 0.3%, Ni: 0.001 to 1.0%, Fe: 0.01 to 2.0%, with the balance being Zn and other unavoidable impurities.

7. The method for improving the quality of transverse fine lines in zinc-aluminum-magnesium thin-coated steel sheets according to claim 6, characterized in that: In step 2), the temperature of the zinc pot is controlled at 390-550°C, based on the melting point of the actual plating solution composition plus 20-50°C, and the temperature of the strip steel entering the zinc pot is controlled at 400-550°C.

8. The method for improving the edge quality of zinc-aluminum-magnesium thick-coated strip steel according to claim 4, characterized in that: In step 3), the strip enters the air knife area. The air source for the air knife is N2 or other inert gas with a purity greater than 99%. The air knife pressure is controlled at 50-900 mbar, the air knife distance is 7-20 mm, the air knife height is 60-600 mm, the air knife angle is 0-3°, and the gap between the air knife baffle and the strip is 2-8 mm.

9. The method for improving the edge quality of zinc-aluminum-magnesium thick-coated strip steel according to claim 4, characterized in that: In step 4), after the air knife exits, the strip enters the post-plating cooling air box, where the cooling rate is 10-50℃ / s. Before entering the top roller, the strip temperature is <280℃. After passing the top roller, the strip enters the post-plating cooling downward section, passes through the cooling fan, and the strip temperature is <100℃. It then enters the quenching tank for cooling, followed by strip leveling, and then coating with a post-treatment film by a roller coater. After drying, it is coiled.

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