Control method for improving thickness precision of hot-based galvanized strip steel

Abstract

The invention relates to the field of hot-rolled strip steel processing, and particularly discloses a control method for improving the thickness precision of hot-based galvanized strip steel. The method comprises the following steps: establishing a finished product thickness calculation model h = H0H1H2H3 + H4H5, wherein key parameters comprise the thinning amount H1 (the thickness lt is 2% * h when the thickness is 3mm, and 3% * h when the thickness is greater than or equal to 3mm) of a scale breaker; the thickness H2 (0.020 mm is taken from 1.8-3.0 mm, gt is taken from 3.0 mm, and 0.030 mm is taken from 3.0 mm) of the pickled oxide scale; the thinning amount H3 of the temper mill is equal to 0.2410.000649 * sigma s (sigma s is yield strength); the equivalent thickness H4 of the zinc layer is equal to 0.000858 + 0.000178 M (M is the adhesion amount of the plating layer); and the thinning amount H5 of the finishing machine is equal to 0. The head and the tail of a hot-rolled raw material are cut by 10 meters, and the thickness H0 of the raw material is reversely deduced to be equal to h + (H1 + H2 + H3H4), so that the thickness tolerance of a finished product is reduced to be within + / -0.05 mm from + / -0.20 mm, and the method is suitable for strip steel with the thickness of 1.8-6.0 mm, the plating layer of 60-450 g / m and the yield strength of 200-800 MPa.

Description

Technical Field

[0001] The invention belongs to the field of hot-dip galvanized (galvanized aluminum-magnesium) steel strips, and particularly relates to a method for improving the thickness precision control of steel strips. Background Art

[0002] Hot-dip galvanizing (galvanized aluminum-magnesium) involves rolling and stretching hot-rolled steel strips with a thickness of 1.5-6.0 mm through a dephosphorization machine to create microcracks in the surface oxide scale. The surface oxide scale is then removed by hydrochloric acid pickling, and the strip surface is cleaned with demineralized water. The strip is then flattened by a skin-pass mill and immersed in molten zinc metal at 450-500°C. Through the solid / liquid interface metallurgical reaction between the strip surface and the liquid zinc metal, a continuous and dense zinc metal coating of a certain thickness is formed on the strip surface, thereby achieving the purpose of corrosion protection.

[0003] Hot-dip galvanizing (galvanized aluminum-magnesium) offers numerous advantages. For example, it protects the entire steel surface, including recessed areas and corners like the inside of pipes. The zinc coating is harder than steel, offering superior wear resistance. Compared to other metal protection methods, it offers unparalleled advantages in its combination of physical barrier and electrochemical protection, coating-to-substrate bonding strength, coating density, durability, maintenance-free operation, cost-effectiveness, and adaptability to product shape and size. Hot-dip galvanizing products are widely used in industries such as construction, electrical cabinets, livestock farming, photovoltaics, and automotive structural components.

[0004] There are two types of galvanized substrates: hot-rolled substrates and cold-rolled substrates. Hot-rolled substrates are relatively low in cost, but the surface is not smooth enough, the thickness accuracy is poor, and the surface after galvanizing is not as smooth as the cold-rolled surface. For cold-rolled galvanized substrates, the substrate is cold-rolled material, which has a smoother surface than hot-rolled material. The surface of the plated material is more beautiful, the thickness accuracy is high, and the corrosion resistance is better. At present, most ordinary galvanized substrates are produced using cold-rolled substrates.

[0005] With the urgent need for enterprises to reduce costs, the demand for hot-dip galvanized sheet to replace cold-dip galvanized sheet is increasing. However, hot-dip galvanized sheet is directly made of hot-rolled sheet as raw material. The thickness accuracy of hot-rolled sheet is about ±0.20mm. Moreover, the thickness of galvanized sheet changes after straightening, pickling, leveling, and galvanizing. It is difficult to control the thickness accuracy of the finished galvanized sheet, and it is difficult to achieve the thickness accuracy requirement of cold-dip galvanized sheet (about ±0.05mm). Therefore, how to control the thickness accuracy of hot-dip galvanized sheet to meet the thickness accuracy requirement of cold-dip galvanized sheet has become a bottleneck problem in replacing cold-dip galvanized sheet with hot-dip galvanized sheet. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for accurately controlling the thickness of hot-base galvanized (galvanized aluminum-magnesium) strip steel to solve the problems of inaccurate thickness control and large thickness deviation of hot-base galvanized strip steel, so as to reduce the thickness accuracy range of hot-base galvanized strip steel to the thickness accuracy range of cold-base galvanized strip steel.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A control method for improving the thickness accuracy of hot-dip galvanized steel strip comprises the following steps: Finished product thickness calculation: Final finished product thickness h = H 0− H 1− H 2− H 3+ H 4− H 5. in, H 0: Hot rolled raw material thickness (mm), H 1: Thinning amount of phosphorus breaking machine (mm), H 2: Thickness of the iron oxide scale removed by pickling (mm), H 3: Thinning amount of the leveling machine (mm), H 4: Equivalent thickness of zinc layer (mm), H 5: Thinning amount of skin-pass machine (mm); Hot rolling raw material control: Based on the thickness of the middle part of the strip, 10 meters of the hot rolled strip is cut off before welding; Calculation of the reduction amount of phosphorus crusher: When the strip thickness is less than 3.0mm, H 1=2%× h ; When the strip thickness is ≥3.0mm, H 1=3%× h ; Determination of pickling scale thickness: When the strip thickness is ≤3.0mm, H 2=0.020mm, when the strip thickness is >3.0mm, H 2=0.030mm; Calculation of thinning amount of leveling machine: H 3=0.241−0.000649× ss ,in ss is the actual yield strength of the strip (MPa); Calculation of equivalent zinc layer thickness: H 4=0.000858+0.000178× M ,in M is the zinc coating adhesion (g / m 2 ); Setting of the thinning amount of the skin-pass machine: H 5=0.

[0008] In the above technical solution, the hot-rolled raw material thickness H0 is based on the thickness of the middle section of the strip. Because the first and last 10 meters of the hot-rolled strip are in a free tension-loss stage, the AGC thickness control accuracy is poor, resulting in significant thickness fluctuations. Generally, the thickness fluctuations at the beginning and end are within ±0.10mm, while the strip body thickness is controlled to a stable within ±0.03mm. To ensure thickness control accuracy, the first and last 10 meters of the hot-rolled strip are cut off during the galvanizing line production process before welding.

[0009] Hot rolled raw material thickness H The formula for determining 0 is: H 0= h +Δ h , Δ h = H 1+ H 2+ H 3− H 4; where Δ h It is the total thinning amount from raw material to finished product (mm).

[0010] Phosphorus breaking machine thickness reduction H 1 , calculated based on the actual elongation of the phosphate crusher. Set the elongation of the phosphate crusher to d =( L - L 0 ) / L 0 , the elongation of the general phosphorus breaking machine is between 2%-3%. For the thickness of the strip steel less than 3.0mm, the grain size of the strip steel is finer, the relative elongation is lower, and the thinning amount is H 1 = d * h = 2%× h For strip steel with thickness ≥3.0mm, the grain size of the strip steel is relatively thin, the relative elongation is large, and the thinning amount is H 1 = d * h =3%× h .

[0011] H 2 :Calculation of the thickness of the iron oxide scale removed by pickling. According to the laboratory measurement of the iron oxide scale on the surface of steel strips of different thicknesses, the thickness of the iron oxide scale of the hot-rolled strip is generally about 10um when the thickness is 1.8-3.0mm, and the thickness of the iron oxide scale of the 3.01-6.0mm strip is about 15um. Since there is iron oxide scale on both the upper and lower surfaces, the thickness of the iron oxide scale removed by pickling is H 2 For strip steel with a thickness of 1.8 mm or less and a thickness of 3.0 mm or less,H 2 0.020mm; for 3.0<thickness≤6.0mm strip steel, H 2 It is 0.030mm.

[0012] H 3 Calculation of the thinning amount of the leveler. The thinning amount of the leveler is proportional to the rolling force of the leveler (rolling force range is generally 5000KN-7000KN) and inversely proportional to the strength of the strip. The thinning amount of different steel grades in the leveler is obtained by fitting the field data: H 3=0.241−0.000649× ss ; s S: The actual yield strength of the strip (unit: MPa).

[0013] H 4 :Calculation of zinc layer thickness Table 1 Equivalent thickness of standard coating of galvanized sheet (unit: mm) For different zinc coating adhesion M, the equivalent thickness of the zinc layer is obtained from Table 1 H 4 . Equivalent thickness of zinc layer H The regression formula of 4 is obtained by fitting statistical production data: H 4=0.000858+0.000178× M .

[0014] H 5 : Thinning amount of skin-pass mill. Since the rolling force of the skin-pass mill is relatively small, about 200KN, the effect on the thickness of the strip is very small. H 5 The thinning amount of the skin-pass machine is zero.

[0015] This method achieves precise control of the thickness of the final product by accurately controlling the thickness of the hot-rolled raw material of hot-dip galvanized (or galvanized aluminum-magnesium) strip. 2 , hot-dip galvanized (or galvanized aluminum-magnesium) steel strip with a yield strength of 200-800MPa can significantly reduce the thickness tolerance of its finished product from ±0.2mm to within ±0.05mm, thereby achieving thickness control accuracy requirements comparable to cold-rolled base galvanized products. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The thinning amount of the leveler according to the present invention H3 Scatter plot of the actual yield strength of the strip.

[0017] Figure 2 The equivalent thickness of the zinc layer in the method of the present invention is H 4 Scatter plot of coating adhesion. DETAILED DESCRIPTION

[0018] The present invention will be further explained below with reference to specific embodiments.

[0019] The core of the hot-dip galvanized strip thickness control method of the present invention lies in accurately calculating the thickness variation of each process step and inferring the target thickness of the hot-rolled raw material. The following is a detailed description of the implementation steps with reference to the following examples: Example 1 (brand DD51D+ZM, finished product thickness 6.0mm, coating 275g / m 2 ) 1. Obtaining raw material parameters Target finished product thickness h =6.0mm, coating adhesion M =275g / m 2 , substrate yield strength ss =290MPa (SPHC hot-rolled raw material); 2. Calculation of key thinning amount Phosphorus breaking machine thickness reduction H 1: Due to thickness ≥3.0mm, take H 1=3%× h =0.03×6.0=0.18mm; Pickling scale thickness H 2: Because the thickness is >3.0mm, take H 2=0.030mm; Thinning amount of leveling machine H 3 : H 3=0.241−0.000649× ss =0.241−0.000649×290=0.0528mm; Equivalent thickness of zinc layer H 4: H 4=0.000858+0.000178× M =0.000858+0.000178×275=0.0498mm; Thinning amount of skin-pass machine H 5=0; 3. Determination of total thinning amount and raw material thickness Total thinning amount: Δ h =H 1+ H 2+ H 3− H 4=0.18+0.030+0.0528−0.0498=0.213mm; Target thickness of hot rolled raw material: H 0= h +Δ h =6.0+0.213=6.213mm; 4. Production verification Using hot-rolled raw material with a thickness of 6.213±0.03mm (after cutting off 10m of the head and tail), the finished product thickness was measured to be 6.01mm, with a tolerance of ±0.01mm (much better than the target of ±0.05mm).

[0020] Example 2 (brand S350GDH+ZM, finished product thickness 2.0mm, coating 150g / m 2 ) 1. Obtaining raw material parameters Target finished product thickness h =2.0mm, coating adhesion M =150g / m 2 , substrate yield strength ss =355MPa (Q355B hot-rolled raw material); 2. Calculation of key thinning amount Phosphorus breaking machine thickness reduction H 1: Because the thickness is less than 3.0mm, take H 1=2%× h =0.02×2.0=0.04mm; Pickling scale thickness H 2: Since 1.8≤thickness≤3.0mm, take H 2=0.020mm; Thinning amount of leveling machine H 3: H 3=0.241−0.000649× ss =0.241−0.000649×355=0.0106mm; Equivalent thickness of zinc layer H 4: H 4=0.000858+0.000178× M =0.000858+0.000178×150=0.0275mm; Thinning amount of skin-pass machine H 5=0; 3. Determination of total thinning amount and raw material thickness Total thinning amount: Δh = H 1+ H 2+ H 3− H 4=0.04+0.020+0.0106−0.0275=0.043mm; Target thickness of hot rolled raw material: H 0= h +Δ h =2.0+0.043=2.043mm; 4. Production verification The product is produced using hot-rolled raw materials with a thickness of 2.043±0.03mm (after cutting off 10m of the head and tail), and the actual thickness of the finished product is 2.02mm, with a tolerance of ±0.02mm.

[0021] Technical Effect Description The above examples prove that: For 1.8-6.0mm thickness, 60-450g / m 2 The thickness tolerance of the finished product of hot-dip galvanized steel strip with coating and yield strength of 200-800MPa is compressed from ±0.20mm of the traditional process to within ±0.05mm; it completely solves the precision defects of hot-dip galvanized sheet caused by fluctuations in raw material thickness and reaches the thickness control level of cold-rolled substrate galvanizing (requirements of national standard GB / T 2518).

Claims

1. A control method for improving the thickness accuracy of hot-dip galvanized steel strip, characterized in that: The following steps are involved: Finished product thickness calculation: Final finished product thickness h = H 0− H 1− H 2− H 3+ H 4− H 5. in, H 0: Hot rolled raw material thickness (mm), H 1: Thinning amount of phosphorus breaking machine (mm), H 2: Thickness of the iron oxide scale removed by pickling (mm), H 3: Thinning amount of the leveling machine (mm), H 4: Equivalent thickness of zinc layer (mm), H 5: Thinning amount of skin-pass machine (mm); Hot rolling raw material control: Based on the thickness of the middle part of the strip, 10 meters of the hot rolled strip is cut off before welding; Calculation of the reduction amount of phosphorus crusher: When the strip thickness is less than 3.0mm, H 1=2%× h ; When the strip thickness is ≥3.0mm, H 1=3%× h ; Determination of pickling scale thickness: When the strip thickness is ≤3.0mm, H 2=0.020mm, when the strip thickness is >3.0mm, H 2=0.030mm; Calculation of thinning amount of leveling machine: H 3=0.241−0.000649× σs ,in σs is the actual yield strength of the strip (MPa); Calculation of equivalent zinc layer thickness: H 4=0.000858+0.000178× M ,in M is the zinc coating adhesion (g / m 2 ); Setting of the thinning amount of the skin-pass machine: H 5=0.

2. The method according to claim 1, characterized in that Hot rolled raw material thickness H The formula for determining 0 is: H 0= h +Δ h ,Δ h = H 1+ H 2+ H 3− H 4; Where, Δ h It is the total thinning amount from raw material to finished product (mm).

3. The method according to claim 1, characterized in that Equivalent thickness of zinc layer H The regression formula of 4 is obtained by fitting statistical production data: H 4=0.000858+0.000178× M ; Applicable coating adhesion range is 60∼450g / m 2 .

4. The method according to claim 1, wherein Thinning amount of leveling machine H The regression formula of 3 is obtained by fitting the measured data: H 3=0.241−0.000649× σs ; Applicable yield strength range is 200∼800MPa.

5. The method according to claim 1, wherein Pickling scale thickness H The value of 2 is based on the hot-rolled strip thickness range: 1.8 ≤ strip thickness ≤ 3.0 mm, H 2=0.020mm; when 3.0<strip thickness≤6.0mm, H 2=0.030mm.

6. The method according to claim 1, characterized in that The method is applicable to: steel strip thickness 1.8 to 6.0 mm; zinc coating weight 60 to 450 g / m 2 ;The thickness tolerance of the finished product is controlled within ±0.05mm.

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