A EPS processing method for hot-rolled coils with excellent cold bending performance

Abstract

The present invention discloses an EPS treatment method for hot-rolled coils with excellent cold-bending performance, and relates to the technical field of surface treatment of automobile steel plates. The present invention discloses an EPS treatment method for hot-rolled coils with excellent cold-bending performance, wherein the metal plate is passed through a slurry jet impeller device, and EPS treatment is performed along the upper and lower symmetrical distribution of the metal plate. The slurry jet impeller device includes slurry impellers fixedly distributed on the upper and lower surfaces of the metal plate, and the impeller is a compressed air shot blasting machine. The slurry impeller is fixed so as to be able to EPS clean the iron oxide layers on the upper and lower surfaces of the metal plate; according to the strength grade of the metal plate material and the cold-bending performance requirements, reasonable EPS process parameters such as slurry jet speed, slurry flow jet incident angle, and strip steel threading speed are further optimized, so that the metal plate obtained after EPS treatment has good cold-bending performance; at the same time, it is beneficial to improve the fatigue performance of the metal plate, and has extremely high application value and economic value.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile steel plate surface treatment, and more particularly to an EPS treatment method for hot-rolled steel coils with excellent cold bending performance. Background Art

[0002] The production of sheet metal generally involves heating, rolling, and cooling processes. In most cases, the surface of the sheet metal must be treated before use to provide a surface suitable for the intended product, allowing for painting or other coatings such as galvanizing or aluminum-silicon plating. The most common method for removing the iron oxide layer from the surface of sheet metal is a "pickling" process. Because pickling is corrosive and polluting, EPS (Electrolyzed Polystyrene) treatment has become widely used in recent years. This treatment removes the iron oxide layer using a slurry (a mixture of water and abrasive) jet.

[0003] EPS (Slurry Jetting) stands for slurry jetting. Its basic principle is to spray a mixture of hard steel grit and water onto the upper and lower surfaces of steel plates. The impact removes the iron oxide scale from the steel surface, leaving the steel plate with a smooth, clean surface. EPS can eliminate pre-treatment steps such as pickling, shot blasting, and painting, achieving green and clean production. However, EPS treatment physically removes the iron oxide layer on the metal surface, and slurry jetting can cause surface damage to the metal sheet. In particular, cold bending performance can be reduced compared to hot-rolled sheet, which can severely affect the material's normal use. In the automotive industry, cold bending performance is a key indicator of material toughness and is closely related to vehicle safety performance, making relevant research of great significance. EPS treatment can cause the surface of hot-rolled coils to become uneven and grooved, reducing the material's formability and fatigue life. This has hindered the market adoption of EPS-treated products, particularly in automotive beam safety components.

[0004] A search revealed relevant patents that address the aforementioned shortcomings. For example, Chinese patent application number 2007800335291, filed on August 27, 2007, and published on August 26, 2009, discloses a slurry spraying device for descaling metal sheets. This device, known as EPS descaling equipment, offers a simpler, chemical-free descaling method, overcoming the shortcomings of existing equipment and methods for descaling metal sheets. The device consists of an uncoiler, a straightener, an EPS processing unit, an oiler, and a coiler. However, no research was conducted into the selection of equipment process parameters and the properties of the descaled material.

[0005] For example, Chinese patent application number 2011800031220, filed on September 13, 2011, and published on September 19, 2012, discloses a method for producing rust-resistant metal plates by descaling them using a slurry jet descaling tank with an improved sand flow. By controlling the slurry discharge rate and the type and amount of sand in the slurry mixture, the metal plates are imbued with rust-resistant properties, eliminating the need for oiling the product for rust prevention. However, the patent does not mention the impact of the improved slurry on the material's various properties.

[0006] Another example is Chinese patent application number 2015106502932, filed on October 9, 2015, and published on March 9, 2016. It discloses a nozzle quick-change device for a strip steel descaling device using abrasive slurry jetting. Multiple abrasive slurry nozzles of the same or different models and specifications are mounted on the circumference of a rotatable nozzle disk. Rotating the nozzle disk allows each nozzle to be connected to the abrasive slurry inlet pipe, enabling automated and rapid nozzle replacement. However, the descaling process and material properties are not described.

[0007] It can be seen that the existing EPS processing technology focuses more on equipment and slurry, and there is little research on the cold bending performance of EPS products. Summary of the Invention

[0008] 1. Technical problem to be solved by the invention

[0009] In view of the problem that there is little research on the cold bending performance of EPS products in existing EPS processing technologies, the present invention proposes an EPS processing method for hot-rolled coils with excellent cold bending performance. According to the strength level of the metal plate and the cold bending performance requirements, the metal plate is passed through the EPS processing unit. The EPS processing unit includes a slurry injection impeller device symmetrically arranged up and down. The slurry injection impeller device is symmetrically distributed along the metal plate up and down for EPS processing. By optimizing reasonable EPS process parameters such as slurry injection speed, slurry flow injection incident angle and strip passing speed, an EPS processed product with excellent cold bending performance is obtained.

[0010] 2. Technical solution

[0011] In order to achieve the above object, the technical solution provided by the present invention is:

[0012] A method for EPS treatment of hot-rolled coils with excellent cold bending performance is disclosed. The method comprises passing the metal sheets through an EPS treatment unit according to the strength level and cold bending performance requirements of the metal sheets. The EPS treatment unit comprises a slurry jet impeller device symmetrically arranged up and down, thereby performing EPS treatment on the surface of the metal sheets to remove the iron oxide layer on the metal surface. During the EPS treatment, the slurry jet speed is 30m / s to 60m / s, the slurry flow rate is 500 to 2500kg / min, the jet incident angle is 80 to 120°, the strip passing speed is 0 to 40m / min, and the surface roughness of the metal sheets after EPS treatment is 2.0 to 5.0um.

[0013] A further technical solution is that for metal sheets with a strength level below 700Mpa, during EPS treatment, the slurry injection speed is preferably 40m / s to 45m / s, the slurry flow rate is preferably 800-1500kg / min, the injection angle is preferably 85-95°, the strip passing speed is preferably 5-25m / min, and the surface roughness of the metal sheet after EPS treatment is 2.5-3.5um. Based on the strength level of the metal sheet material and the cold bending performance requirements, the EPS process parameters such as the slurry injection speed, slurry flow injection angle, and strip passing speed are further optimized to ensure that the metal sheet obtained after EPS treatment has good cold bending performance. At the same time, it is beneficial to improve the fatigue performance of the metal sheet and has extremely high application value and economic value.

[0014] A further technical solution is that the slurry jet impeller device includes a slurry impeller. After the slurry impeller is fixedly distributed on the upper and lower surfaces of the metal plate, the strip moves at a certain speed, and the slurry impeller starts to spray slurry to perform EPS treatment on the upper and lower surfaces of the metal plate. The metal plate after EPS treatment is oiled for corrosion protection and or coiled for subsequent processing.

[0015] According to a further technical solution, the impeller equipment is a compressed air shot blasting machine.

[0016] According to a further technical solution, the slurry is a mixture of water and a slurry abrasive, the slurry abrasive is cast steel sand, and the hardness of the cast steel sand is 46 to 65 HRC.

[0017] According to a further technical solution, the hardness of the cast steel sand is 55-60HRC.

[0018] 3. Beneficial effects

[0019] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0020] (1) The present invention provides an EPS processing method for hot-rolled coils with excellent cold bending performance. According to the strength level and cold bending performance requirements of the metal sheet, the metal sheet is passed through an EPS processing unit. The EPS processing unit includes a slurry injection impeller device symmetrically arranged up and down. The slurry injection impeller device is symmetrically distributed along the metal sheet to perform EPS processing. By optimizing reasonable EPS process parameters such as slurry injection speed, slurry flow injection incident angle, and strip passing speed, the metal sheet obtained after EPS processing has good cold bending performance. At the same time, it is beneficial to improve the fatigue performance of the metal sheet, and has extremely high application value and economic value.

[0021] (2) The present invention provides an EPS treatment method for hot-rolled coils with excellent cold bending performance. The slurry jet impeller device includes a slurry impeller. Several slurry impellers are fixedly distributed on the upper and lower surfaces of the metal plate. The fixing method is not particularly limited, and the EPS treatment is based on the ability to clean the iron oxide layer on the upper and lower surfaces of the metal plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 (a) The cold bending test results of Example 1 of the present invention and (b) the metallographic photograph of the arc cross section of the cold bending test;

[0023] Figure 2 The cold bending test results (a) and the metallographic photograph (b) of the arc cross section of the cold bending test of Comparative Example 1 of the present invention are shown;

[0024] Figure 3 The results of the cold bending test at a bending angle of 120° for comparative example 1 are shown;

[0025] Figure 4 The results of the cold bending test at a bending angle of 90° for comparative example 1 are shown;

[0026] Figure 5 This is a metallographic photograph of the arc cross section of the cold bending test in Example 2;

[0027] Figure 6 This is a metallographic photograph of the arc cross section of the cold bending test in comparative example 2. DETAILED DESCRIPTION

[0028] In order to further understand the content of the present invention, the invention is described in detail with reference to the accompanying drawings.

[0029] According to the strength level and cold bending performance requirements of the metal sheet, the metal sheet is passed through the EPS processing unit, and the EPS processing unit includes a slurry injection impeller device symmetrically arranged up and down, so as to perform EPS treatment on the surface of the metal sheet to remove the iron oxide layer on the metal surface; during the EPS treatment, the slurry injection speed is 30m / s~60m / s, the slurry flow rate is 500~2500kg / min, the injection incident angle is 80~120°, the strip passing speed is 0~40m / min, and the surface roughness of the metal sheet after EPS treatment is 2.0~5.0um; according to the strength level and cold bending performance requirements of the metal sheet, the metal sheet is passed through the slurry injection impeller device, and EPS treatment is performed along the metal sheet symmetrically distributed up and down, so as to obtain an EPS treated product with excellent cold bending performance.

[0030] For metal sheets with a strength level below 700Mpa, during EPS treatment, the slurry spraying speed is preferably 40m / s to 45m / s, the slurry flow rate is preferably 800 to 1500kg / min, the spraying incident angle is preferably 85 to 95°, the strip passing speed is preferably 5 to 25m / min, and the surface roughness of the metal sheet after EPS treatment is 2.5 to 3.5um. According to the strength level of the metal sheet material and the cold bending performance requirements, reasonable EPS process parameters such as slurry spraying speed, slurry flow rate spraying incident angle and strip passing speed are further optimized, so that the metal sheet obtained after EPS treatment has good cold bending performance; at the same time, it is beneficial to improve the fatigue performance of the metal sheet and has extremely high application value and economic value. The slurry spraying impeller device includes a slurry impeller, which is fixedly distributed on the upper and lower surfaces of the metal sheet. The strip moves at a certain speed, and the slurry impeller starts to spray slurry to perform EPS treatment on the upper and lower surfaces of the metal sheet. The metal sheet after EPS treatment is oiled for corrosion protection and or coiled for subsequent processing.

[0031] In this embodiment, the impeller is a compressed air shot blasting machine. The method for securing the slurry impeller is not particularly limited, provided that the EPS can cleanly remove the iron oxide layers on the upper and lower surfaces of the metal sheet. The slurry is a mixture of water and a slurry abrasive, wherein the slurry abrasive is cast steel grit, and the hardness of the cast steel grit is 46 to 65 HRC.

[0032] Furthermore, the hardness of the cast steel sand is 55-60HRC.

[0033] Example 1

[0034] The EPS processing method for hot-rolled coil with excellent cold bending performance in this embodiment has a metal plate yield strength of 540 MPa, a material thickness of 8 mm, and a cold bending performance transverse sample d=a (d is the bending diameter, a is the sample thickness).

[0035] Eight compressed air slurry impellers are symmetrically distributed along the upper and lower sides of the metal plate. The EPS treatment process parameters are: slurry injection speed of 43m / s, slurry flow rate of 950kg / min, injection incident angle of 90°, slurry injection strip coverage of 100%, strip passing speed of 15m / min, slurry abrasive is cast steel sand with a hardness of 58HRC, and the surface roughness after EPS treatment is 3.0um.

[0036] Comparative Example 1

[0037] Eight compressed air slurry impellers are symmetrically distributed along the upper and lower sides of the metal plate. The EPS treatment process parameters are as follows: slurry spraying speed of 50m / s, slurry flow rate of 1200kg / min, spraying incident angle of 90°, slurry spraying strip coverage of 100%, strip passing speed of 10m / min, slurry abrasive is cast steel sand with a hardness of 58HRC, and the surface roughness after EPS treatment is 4.0um.

[0038] The cold bending properties of the metal sheets obtained in Example 1 and Comparative Example 1 were tested:

[0039] Take a transverse sample of 120*35mm and carry out a cold bending test according to the bending radius d=a and the bending angle 180°. The outer side of the bending radius of the cold-bent sample of Example 1 is smooth and crack-free, while the outer side of the bending radius of the cold-bent sample of Comparative Example 1 has a coarsened surface texture. Further metallographic analysis shows that Figure 1 and 2 As shown, there are micro cracks on the metal surface; further changing the bending angle of the cold bending test of comparative example 1, the test results are as follows Figure 3 and 4 As shown, the outer side of the bending radius of the cold-bent specimen with a bending angle of 120° is visible with coarsened surface texture; the outer side of the bending radius of the cold-bent specimen with a bending angle of 90° is smooth without coarsened surface texture.

[0040] Example 2

[0041] This embodiment provides an EPS processing method for hot-rolled coils with excellent cold bending performance. The basic structure is the same as that of Example 1, with the following differences and improvements: the metal sheet has a yield strength of 472 MPa, a material thickness of 5 mm, and a cold bending performance transverse test specimen d = 0.5a (d is the bending diameter, a is the specimen thickness);

[0042] Eight compressed air slurry impellers are symmetrically distributed along the upper and lower parts of the metal plate. The EPS treatment process parameters are as follows: slurry spraying speed of 40m / s, slurry flow rate of 900kg / min, spraying incident angle of 90°, slurry spraying strip coverage of 100%, strip passing speed of 20m / min, slurry abrasive is cast steel sand with a hardness of 58HRC, and the surface roughness after EPS treatment is 2.8um.

[0043] Comparative Example 2

[0044] Eight compressed air slurry impellers are symmetrically distributed along the upper and lower sides of the metal plate. The EPS treatment process parameters are as follows: slurry spraying speed of 55m / s, slurry flow rate of 1500kg / min, spraying incident angle of 90°, slurry spraying strip coverage of 100%, strip passing speed of 12m / min, slurry abrasive is cast steel sand with a hardness of 58HRC, and the surface roughness after EPS treatment is 4.6um.

[0045] The cold bending properties of the metal sheets obtained in Example 2 and Comparative Example 2 were tested:

[0046] Take a transverse specimen of 120*35mm and carry out a cold bending test according to the bending radius d=a and the bending angle 180°. Figure 5 and 6 As shown, the outer side of the bending radius of the cold-bent specimen of Example 2 is smooth and free of cracks, while the surface texture of the outer side of the bending radius of the cold-bent specimen of Comparative Example 2 is coarsened, and microcracks exist on the metal surface.

[0047] The above results show that the metal sheet obtained by the EPS treatment method for hot-rolled plate with excellent cold bending performance provided by the present invention has good cold bending performance, and at the same time, is beneficial to improving the fatigue performance of the material, and has extremely high application value and economic value.

[0048] The above is a schematic description of the present invention and its embodiments, which is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs a structure and embodiment similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A method for treating EPS of hot-rolled coils, characterized by: According to the strength level and cold bending performance requirements of the metal sheet, the metal sheet is passed through the EPS processing unit, and the EPS processing unit includes a slurry injection impeller device arranged symmetrically up and down along the metal sheet to perform EPS processing; During EPS treatment, the slurry spraying speed is 40m / s~45m / s, the slurry flow rate is 800~950kg / min, the spraying incident angle is 85~95°, the metal sheet passing speed is 15~25m / min, and the surface roughness of the metal sheet after EPS treatment is 2.0~5.0μm; The slurry jet impeller device includes a compressed air slurry impeller, and the slurry impellers are fixedly distributed on the upper and lower surfaces of the metal plate. The metal plate moves forward at a certain speed, and the slurry impeller starts to spray slurry to perform EPS treatment on the upper and lower surfaces of the metal plate. The metal plate after EPS treatment is oiled for corrosion protection and coiled for subsequent processing; The slurry is a mixture of water and slurry abrasive, the slurry abrasive is cast steel sand, and the hardness of the cast steel sand is 55-60HRC.

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