Method for controlling quality of aluminum-silicon thin coating of open-fire continuous annealing furnace

Abstract

The invention discloses a quality control method for an aluminum-silicon thin coating of an open-fire continuous annealing furnace, and belongs to the field of open-fire continuous annealing furnaces and hot-dip aluminum-silicon. The method comprises the steps of acid pickling, cold rolling, cleaning and continuous annealing. The conductivity of alkali liquor used in the cleaning process is 55-60 ms / cm, and the current density of the electrolysis section is 25-38 A; the continuous annealing process comprises an open fire section, a first heating section, a second heating section and a cold spraying section; the coefficient of excess air of the main burner of the open fire section is controlled to be 95%-98%; in an open fire continuous annealing furnace area, the O2 content is controlled to be smaller than or equal to 10 ppm, and the hot dew point is-60 DEG C to-70 DEG C; the H2 flow of the second heating section is larger than or equal to 55 nm < 3 > / h; and the H2 flow of the first heating section and the cold spraying section is larger than or equal to 102 nm < 3 > / h. According to the invention, the surface quality of the hot-dip aluminum-silicon plated product is improved.

Description

Technical Field

[0001] The present invention belongs to the field of open flame continuous annealing furnace and hot-dip aluminum silicon, and relates to a method for improving the quality of aluminum silicon thin coating products; and can be applied to a method for controlling the quality improvement of strip steel coating. Background Art

[0002] In recent years, as the automotive and home appliance industries have increasingly demanded higher quality steel for cold-rolled strip, the use of high-strength and ultra-high-strength steel has increased year by year. Hot-dip aluminum-silicon (Al-10wt%Si) products are highly favored by home appliance manufacturers, automotive OEMs, and stamping plants due to their stable coating properties and excellent heat resistance, corrosion resistance, heat reflectivity, and environmental friendliness after stamping and deformation. The production process for hot-dip aluminum-silicon products primarily involves the following steps: pickling – cold rolling – cleaning – continuous annealing – hot-dip aluminum-silicon coating – cooling – skin-passing and straightening. Due to the limitations of the mill structure, "missing plating defects" in hot-formed steel with thin aluminum-silicon coatings are difficult to control. The resulting aluminum-silicon-coated steel sheets exhibit coarse aluminum flakes and frequent defects such as missing plating, zinc slag, and chromium marks. These defects not only affect the product's aesthetics, but also reduce its corrosion resistance, shorten its service life, and degrade its quality, failing to meet customers' high surface quality requirements.

[0003] Therefore, in order to improve the surface quality of hot-dip aluminum-silicon products, further reduce the difficulty of production control, and improve production efficiency, it is necessary to provide a quality control method for aluminum-silicon thin coatings. Summary of the Invention

[0004] The purpose of the present invention is to provide a quality control method for aluminum-silicon thin coatings in an open flame continuous annealing furnace. Based on the existing equipment level, through in-depth research and innovation on the optimization of the cleaning section, the function of the continuous annealing furnace and the process parameters, without significantly increasing the equipment investment, the method can achieve fine control of key process parameters, reduce surface defects of finished products, ensure that product quality is stable and controlled, and meet quality requirements.

[0005] A quality control method for aluminum-silicon thin coatings in an open flame continuous annealing furnace, comprising pickling-cold rolling-cleaning-continuous annealing; The conductivity of the alkali solution used in the cleaning process is 55~60ms / cm, and the current density of the electrolysis section is 25~38A; The continuous annealing process includes open flame section - heating section one - heating section two - spray cooling section; The "excess air coefficient" of the main burner in the open flame section is controlled at 95%~98%; The O2 content in the open flame continuous annealing furnace area is controlled to ≤10ppm to ensure the airtightness of the open flame continuous annealing furnace area; the thermal dew point is -60~-70℃; H2 flow rate of heating section 2 ≥ 55nm 3 / h, preferably 55~60nm3 / h; H2 flow rate in the heating section and the spray cooling section ≥ 102nm 3 / h, preferably 102~115nm 3 / h.

[0006] Furthermore, the alkali solution is sodium hydroxide solution.

[0007] Furthermore, the medium discharge during the cleaning process: the alkali washing and brushing tank tank liquid accounts for 10%~20% of the tank volume per 5h.

[0008] Furthermore, the O2 content in the nose of the open flame continuous annealing furnace is controlled to be ≤10ppm, and the flange bolts are tightened after the aluminum silicon plating solution is hot-lifted into the pot.

[0009] Furthermore, the H2 content in the furnace in the heating section and the spray cooling section is ≥10%, preferably 10~15%.

[0010] Furthermore, before plating the aluminum-silicon thin layer, if the pot does not contain aluminum-silicon plating solution and the plating solution needs to be replaced, the furnace area should be "maintained at positive pressure" during the shutdown of the rotary pot.

[0011] Furthermore, the thickness of the aluminum silicon thin coating is 0.015-0.025 mm.

[0012] Furthermore, after continuous annealing, the steel is hot-dip coated with aluminum silicon, cooled, polished and straightened.

[0013] Furthermore, between the hot-dip aluminum-silicon coating and cooling process, aluminum powder spraying is also included.

[0014] Furthermore, the feeding amount of aluminum powder is 30%~50%, and the strip temperature at the entrance of the aluminum powder box is 610~615℃.

[0015] Furthermore, aluminum powder is sprayed using a "small aluminum flower" device.

[0016] Beneficial effects of the present invention: 1. By optimizing the process parameters of the cleaning section and open flame continuous annealing furnace, the present invention reduces surface defects in finished products without significantly increasing equipment investment, thereby improving the surface quality of hot-dip aluminum-silicon products and further increasing the product yield: after the implementation of the present invention, the yield rate of "aluminum-silicon thin coating" has increased from the previous 30% (degradation due to plating defects) to the current 91%.

[0017] 2. By reducing quality waste, costs are reduced and economic benefits are improved.

[0018] Create economic benefits as follows: a. AlSi thin coating - expected production: 200t / month in 2024 and 500t / month in 2025; after implementation of this invention, 200t of quality waste can be reduced per month; b. The price difference between authentic AlSi thin-coated materials and scrap steel is 2,500 yuan / t. After the implementation of the present invention, the quality scrap can be reduced by 200t / month. The contribution coefficient of the galvanizing process is calculated as 0.6. The monthly cost reduction amount = 200t*2,500 yuan / t*0.6=300,000 yuan, and the estimated annual profit amount = 3.6 million yuan. DETAILED DESCRIPTION

[0019] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0020] Example 1 A quality control method for aluminum silicon thin coating in open flame continuous annealing furnace, steel grade: AC1500HS+AS, roll number: AF5604410A00, specification: 1.396*1405mm, coating: 60g / m 2 The method includes pickling - cold rolling - cleaning - continuous annealing - hot-dip aluminum silicon coating - cooling - skin straightening and straightening; the continuous annealing process includes open flame section - heating section - heating section - spray cooling section; 1. Air tightness control of open flame continuous annealing furnace area + furnace nose: 1. Air tightness of furnace nose: O2 content ≤ 10ppm, and “flange bolts are tightened” after the aluminum silicon plating solution is heated up; 2. Air tightness of furnace area: O2 content ≤10ppm, thermal dew point ℃: -60~-70℃, the furnace area "maintains positive pressure" during the shutdown of the rotary pot to reduce O2 infiltration.

[0021] 2. Control of process parameters during cleaning process: 1. Alkali section: sodium hydroxide solution, conductivity 55~60ms / cm; 2. Current density of electrolysis section: 25~38A; 3. Cleaning section medium discharge: Alkaline cleaning and brushing tank tank liquid accounts for 10%~20% of the tank volume per 5h.

[0022] 3. Air-fuel ratio control of the open flame section of the open flame continuous annealing furnace: The "excess air coefficient" of the main burner in the open flame section is controlled at 95%~98%.

[0023] 4. H2 flow control in open flame continuous annealing furnace: 1. Heating stage 2: H2 flow rate 55~60nm 3 / h; 2. Heating section and cooling section: H2 flow rate 102~115nm 3 / h (H2 content 10~15%).

Claims

1. A method for controlling the quality of aluminum-silicon thin coatings in an open flame continuous annealing furnace, characterized in that: The method comprises pickling-cold rolling-cleaning-continuous annealing; The conductivity of the alkali solution used in the cleaning process is 55~60ms / cm, and the current density of the electrolysis section is 25~38A; The continuous annealing process includes open flame section - heating section one - heating section two - spray cooling section; The excess air coefficient of the main burner in the open flame section is controlled at 95%~98%; The O2 content in the open flame continuous annealing furnace area is controlled to be ≤10ppm; the thermal dew point is -60~-70℃; H2 flow rate of heating section 2 ≥ 55nm 3 / h; H2 flow rate in the heating section and the spray cooling section ≥ 102nm 3 / h.

2. The method according to claim 1, characterized in that Lye is a sodium hydroxide solution.

3. The method according to claim 1, characterized in that Medium discharge during cleaning process: Alkaline washing and brush washing tank liquid accounts for 10%~20% of the tank volume per 5h.

4. The method according to claim 1, wherein The O2 content in the nose of the open flame continuous annealing furnace is controlled to be ≤10ppm, and the flange bolts are tightened after the aluminum silicon plating solution is hot.

5. The method according to claim 1, wherein The H2 content in the furnace in the heating section and the cooling section is ≥10%.

6. The method according to claim 1, characterized in that Before plating the aluminum-silicon thin layer, if there is no aluminum-silicon plating solution in the pot and the plating solution needs to be replaced, the furnace area should maintain positive pressure during the pot stop period.

7. The method according to claim 1, characterized in that The thickness of the aluminum silicon thin coating is 0.015-0.025 mm.

8. The method according to claim 1, characterized in that After continuous annealing, it is hot-dip coated with aluminum silicon, cooled, skin-finished and straightened.

9. The method according to claim 1, characterized in that Between the hot-dip aluminum-silicon coating and cooling process, aluminum powder spraying is also included.

10. The method according to claim 9, characterized in that The aluminum powder feeding amount is 30%~50%, and the strip temperature at the aluminum powder box entrance is 610~615℃.