Production method of high-grade surface-galvanized automobile outer plate

Abstract

The invention belongs to the technical field of steel rolling, and discloses a production method of an automobile sheet with a high-grade surface, which comprises the following steps: (1) before an outer plate is produced, setting the temperature of molten zinc to be 455-465 DEG C, and setting the temperature of the molten zinc in transition to be 5-10 DEG C below the temperature of the molten zinc; when the temperature of the molten zinc is reduced by 5-10 DEG C, the temperature of the molten zinc in the transition roll is set to be consistent with the current temperature of the molten zinc, and then the transition roll is used for slagging-off and slag salvaging; (2) when the outer plate is produced, the temperature of the outer plate entering the molten zinc is adjusted to be 5-10 DEG C higher than the temperature of the molten zinc before slagging-off of the transition roll in the step (1); and when the temperature of the molten zinc is 5-10 DEG C higher than the temperature of the molten zinc before slagging off of the transition roll in the step (1), the temperature of the outer plate entering the molten zinc is adjusted to be consistent with the current temperature of the molten zinc. The method can control the surface defects of the strip steel and meet the requirement of automobile users for high surface quality of the outer plate.

Description

Technical Field

[0001] The present invention belongs to the technical field of automotive sheet production, and particularly relates to a production method for high-grade surface galvanized automotive outer panels. Background Art

[0002] Automotive outer panels have high requirements for coating performance, and the surface quality of galvanized sheets directly affects subsequent coating. The most difficult problems to solve in the production process of automotive outer panels are Figure 1 、 Figure 2 the zinc slag and small black dot defects (micro-zinc slag) shown in the figure. In the current production methods of outer panels, only raising the pot temperature is proposed, which can reduce the generation of zinc slag and small black dots, but the method is vague and has poor operability, resulting in unstable production of outer panels; on the other hand, some manufacturers can only control slag during the roll change and maintenance process of the immersion rolls. When the Fe content in the zinc liquid is not saturated, outer panels are produced in the first 1 - 3 days of the initial cycle of the rolls and cannot be produced at other times, otherwise the outer panels will be downgraded due to insufficient slag control, resulting in a low output of outer panels on the entire production line. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a production method for high-grade surface galvanized automotive outer panels, which can control the surface defects of the strip steel and meet the requirements of automotive users for high surface quality of the outer panels.

[0004] To achieve the above object, the present invention adopts the following technical solutions: A production method for high-grade surface galvanized automotive outer panels, comprising the following steps: (1) Before the production of the outer panel, the zinc liquid temperature is 455 - 465°C, and the zinc liquid temperature of the transition coil is set 5 - 10°C below the zinc liquid temperature; when the zinc liquid temperature drops by 5 - 10°C (the zinc liquid temperature is not lower than the transition coil temperature), the zinc liquid temperature of the transition coil is set to be the same as the current zinc liquid temperature, and then the transition coil is used for slag skimming and slag fishing; (2) During the production of the outer panel, the zinc liquid temperature of the outer panel is adjusted to be 5 - 10°C higher than the zinc liquid temperature before the slag skimming of the transition coil in step (1); when the zinc liquid temperature is 5 - 10°C higher than the zinc liquid temperature before the slag skimming of the transition coil in step (1) (the zinc liquid temperature is not higher than the outer panel temperature), the zinc liquid temperature of the outer panel is adjusted to be the same as the current zinc liquid temperature.

[0005] Further, in step (1) of the present invention, 1 transition coil is used for slag skimming and slag fishing.

[0006] Further, the method of the present invention determines the end time of the current round of outer panel production according to the strip steel speed v, specifically as follows: When 95 m / min ≤ strip steel speed v ≤ 105 m / min, except for the current coil, produce 1 more coil of outer panel, and then end the production of the current round of outer panel; When 105 m / min < strip speed v < 115 m / min, after the current coil production is completed by 50% or more, produce 1 or 2 coils of outer panel and then end the current round of outer panel production; When 115 m / min ≤ strip speed v ≤ 125 m / min, produce 2 coils of outer panel in addition to the current coil and then end the current round of outer panel production.

[0007] Furthermore, in the zinc bath of the present invention, the Al content is 0.2 - 0.27%, the Fe content is 0.08 - 0.12%, and the strip thickness is 0.7 - 0.85 mm.

[0008] The invention principle and beneficial technical effects of the technical solution of the present invention are as follows: The present invention utilizes the different saturated solubilities of Fe in the zinc bath at different temperatures. For example, Figure 3 and Figure 4 As shown, the phases of the same component in the zinc bath at 450 °C and 460 °C are different; at 450 °C, 0.01% Fe and 0.2% Al are in a two-phase region where liquid phase and Fe2AL5 (suspended slag) coexist, while at 460 °C, the above components are in a single liquid phase region.

[0009] Within a certain temperature range, the higher the zinc bath temperature, the greater the saturated solubility of Fe, but the Fe loss of the strip in the zinc bath also increases with the increase in temperature. Especially when it reaches around 470 - 480 °C, the Fe loss shows an exponential increase, as Figure 5 shown. Therefore, the zinc bath temperature should be controlled within a reasonable range.

[0010] The present invention adjusts the zinc bath temperature before and after the outer panel production through the strip's own temperature to control the generation and precipitation of zinc slag, thereby obtaining high-grade surface galvanized automotive outer panels. First, cool down the original zinc bath temperature by adjusting the temperature of the transitional coil entering the zinc bath, reducing the saturated solubility of Fe in the zinc bath and generating zinc slag. Then, remove the zinc slag in the zinc bath through slag skimming and the transitional coil. Compared with heating and production at a lower zinc bath temperature, reducing the zinc bath temperature can quickly generate a large amount of zinc slag and form slag, enabling the originally small and difficult-to-remove suspended slag to aggregate into large zinc slag, greatly reducing the number of tiny suspended slag in the zinc bath, thereby achieving the purpose of quickly reducing the Fe content in the zinc bath. Subsequently, heat the zinc bath by increasing the strip temperature entering the zinc bath, increasing the saturated solubility of Fe in the zinc bath, creating a Fe unsaturated window period, and effectively reducing the generation of zinc slag. Finally, according to the strip production speed, estimate the Fe increase rate and the time when the zinc bath reaches saturation after heating, so as to give an accurate outer panel production timing, making the outer panel production method precise and operable.

[0011] The method of the present invention is practical and effective, which can realize the production of outer plates in the whole cycle of sink rolls, improve the outer plate production capacity of the production line, and at the same time meet the requirements of automobile users for the high surface quality of outer plates. Description of the Drawings

[0012] Figure 1 It is a macroscopic diagram of zinc slag defects; Figure 2 It is a macroscopic diagram of small black dot (micro zinc slag) defects; Figure 3 It is an isothermal diagram of Zn-Al-Mg at 450°C; Figure 4 It is an isothermal diagram of Zn-Al-Mg at 460°C; Figure 5 It is a diagram of the change of strip Fe loss with the temperature of zinc liquid. Detailed Embodiments

[0013] The present invention will be further described in detail below in conjunction with specific embodiments. Embodiment 1

[0014] The steel grade of the automobile outer plate in this embodiment is DC56D+Z, the specification is 0.75*1200mm, the coating is Z120, and its production method is as follows: (1) Before the production of the outer plate, the Al content in the zinc liquid is 0.27%, the Fe content is 0.08%, the temperature of the zinc liquid is 455°C, and the temperature of the transition roll-in zinc liquid is adjusted to 445°C; when the temperature of the zinc liquid drops to 450°C, the temperature of the transition roll-in zinc liquid is adjusted to 450°C, and then the current parameters are maintained unchanged, and 1 transition roll is used for slag skimming and slag fishing.

[0015] (2) During the production of the outer plate, the temperature of the outer plate roll-in zinc liquid is adjusted to 460°C, and when the temperature of the zinc liquid reaches 460°C, the temperature of the outer plate roll-in zinc liquid is maintained at 460°C.

[0016] The production speed of the strip is 125m / min. Except for the current roll, 2 more rolls of strip will be produced to end the production of the outer plate in this round.

[0017] The surface defects of the automobile outer plate produced in this embodiment meet the requirements of Class "05" in the DIN1623-2009 standard. Embodiment 2

[0018] The steel grade of the automobile outer plate in this embodiment is DX53D+Z, the specification is 0.75*1300mm, the coating is Z120, and its production method is as follows: (1)Before the production of the outer panel, the Al content in the zinc bath is 0.24%, the Fe content is 0.09%, the temperature of the zinc bath is 460 °C, and the temperature of the transition coil being fed into the zinc bath is adjusted to 450 °C; when the temperature of the zinc bath drops to 455 °C, the temperature of the transition coil being fed into the zinc bath is adjusted to 455 °C, and then the current parameters are maintained unchanged. Use 1 transition coil for slag skimming and slag removal.

[0019] (2)During the production of the outer panel, the temperature of the outer panel being fed into the zinc bath is adjusted to 460 °C, and when the temperature of the zinc bath reaches 460 °C, the temperature of the outer panel being fed into the zinc bath is maintained at 460 °C.

[0020] The production speed of the strip is 115 m / min. Except for the current coil, 2 more coils of strip will be produced subsequently to end the production of the outer panel for this round.

[0021] The surface defects of the automotive outer panel produced in this example meet the requirements of Grade "05" in the DIN1623 - 2009 standard. Example 3

[0022] The steel grade of the automotive outer panel in this example is HC180BH+Z, the specification is 0.75 * 1500 mm, and the coating is Z100. The production method is as follows: (1)Before the production of the outer panel, the Al content in the zinc bath is 0.22%, the Fe content is 0.11%, the temperature of the zinc bath is 465 °C, and the temperature of the transition coil being fed into the zinc bath is adjusted to 460 °C; when the temperature of the zinc bath drops to 460 °C, the temperature of the transition coil being fed into the zinc bath is adjusted to 460 °C, and then the current parameters are maintained unchanged. Use 1 transition coil for slag skimming and slag removal.

[0023] (2)During the production of the outer panel, the temperature of the outer panel being fed into the zinc bath is adjusted to 470 °C, and when the temperature of the zinc bath reaches 465 °C, the temperature of the outer panel being fed into the zinc bath is adjusted to 465 °C.

[0024] The production speed of the strip is 120 m / min. Except for the current coil, 2 more coils of strip will be produced subsequently to end the production of the outer panel for this round.

[0025] The surface defects of the automotive outer panel produced in this example meet the requirements of Grade "05" in the DIN1623 - 2009 standard. Example 4

[0026] The steel grade of the automotive outer panel in this example is DC53D+Z, the specification is 0.85 * 1450 mm, and the coating is Z100. The production method is as follows: (1)Before the production of the outer panel, the Al content in the zinc bath is 0.23%, the Fe content is 0.09%, the temperature of the zinc bath is 460 °C, and the temperature of the transition coil being fed into the zinc bath is adjusted to 451 °C; when the temperature of the zinc bath drops to 453 °C, the temperature of the transition coil being fed into the zinc bath is adjusted to 453 °C, and then the current parameters are maintained unchanged. Use 1 transition coil for slag skimming and slag removal.

[0027] (2)During the production of the outer panel, adjust the temperature of the outer panel being immersed in the zinc bath to 460°C. When the zinc bath temperature reaches 460°C, maintain the temperature of the outer panel being immersed in the zinc bath at 460°C.

[0028] The production speed of the strip is 95 m / min. Except for the current coil, one more coil of strip will be produced later to end the production of the outer panel for this round.

[0029] The surface defects of the automotive outer panel produced in this embodiment meet the requirements of Class "05" in the DIN1623 - 2009 standard. Example 5

[0030] The steel grade of the automotive outer panel in this embodiment is DX56D+Z, the specification is 0.85*1250 mm, and the coating is Z100. Its production method is as follows: (1)Before the production of the outer panel, the Al content in the zinc bath is 0.20%, the Fe content is 0.12%, the zinc bath temperature is 457°C, and adjust the temperature of the transitional immersion in the zinc bath to 450°C; when the zinc bath temperature drops to 450°C, adjust the temperature of the transitional immersion in the zinc bath to 450°C, then maintain the current parameters unchanged, and use 1 transitional coil for slag skimming and slag removal.

[0031] (2)During the production of the outer panel, adjust the temperature of the outer panel being immersed in the zinc bath to 460°C. When the zinc bath temperature reaches 457°C, adjust the temperature of the outer panel being immersed in the zinc bath to 457°C.

[0032] The production speed of the strip is 100 m / min. Except for the current coil, one more coil of strip will be produced later to end the production of the outer panel for this round.

[0033] The surface defects of the automotive outer panel produced in this embodiment meet the requirements of Class "05" in the DIN1623 - 2009 standard. Example 6

[0034] The steel grade of the automotive outer panel in this embodiment is DX56D+Z, the specification is 0.8*1550 mm, and the coating is Z100. Its production method is as follows: (1)Before the production of the outer panel, the Al content in the zinc bath is 0.22%, the Fe content is 0.10%, the zinc bath temperature is 460°C, and adjust the temperature of the transitional immersion in the zinc bath to 452°C; when the zinc bath temperature drops to 455°C, adjust the temperature of the transitional immersion in the zinc bath to 455°C, then maintain the current parameters unchanged, and use 1 transitional coil for slag skimming and slag removal.

[0035] (2)During the production of the outer panel, adjust the temperature of the outer panel being immersed in the zinc bath to 464°C. When the zinc bath temperature reaches 464°C, maintain the temperature of the outer panel being immersed in the zinc bath at 464°C.

[0036] The production speed of the strip steel is 105 m / min. Except for the current coil, one more coil of strip steel will be produced subsequently to end the production of the outer panel in this round.

[0037] The surface defects of the automotive outer panel produced in this embodiment meet the requirements of Class "05" in the DIN1623 - 2009 standard. Example 7

[0038] The steel grade of the automotive outer panel in this embodiment is HC180BH+Z, the specification is 0.8*1150 mm, and the coating is Z100. Its production method is as follows: (1) Before the production of the outer panel, the Al content in the zinc bath is 0.21%, the Fe content is 0.11%, the temperature of the zinc bath is 457 °C, the temperature of the transition coil entering the zinc bath is adjusted to 450 °C. When the temperature of the zinc bath drops to 452 °C, the temperature of the transition coil entering the zinc bath is adjusted to 452 °C, and then the current parameters are maintained unchanged. One transition coil is used for slag skimming and dross fishing.

[0039] (2) During the production of the outer panel, the temperature of the outer panel coil entering the zinc bath is adjusted to 462 °C. When the temperature of the zinc bath reaches 457 °C, the temperature of the outer panel coil entering the zinc bath is adjusted to 457 °C.

[0040] The production speed of the strip steel is 110 m / min, and 60% has been produced. One more coil of strip steel will be produced subsequently to end the production of the outer panel in this round.

[0041] The surface defects of the automotive outer panel produced in this embodiment meet the requirements of Class "05" in the DIN1623 - 2009 standard.

[0042] The above description is only the basic principle of the present invention and does not impose any limitation on the present invention. Any equivalent changes and modifications made based on the present invention are within the scope of the patented technology protection scheme.

[0043] The technical parts not detailed in the present invention are all well-known technologies.

Claims

1. A production method of a high-grade galvanized automotive outer panel, characterized in that, It includes the following steps: (1) Before the production of the outer plate, the temperature of the zinc bath is 455 - 465 °C, and the temperature of the transition roll-in zinc bath is set 5 - 10 °C below the temperature of the zinc bath; after the temperature of the zinc bath drops by 5 - 10 °C, the temperature of the transition roll-in zinc bath is set to be the same as the current zinc bath temperature, and then the transition roll is used for skimming and dross removal; (2) During the production of the outer plate, the temperature of the outer plate entering the zinc bath is adjusted to be 5 - 10 °C higher than the temperature of the zinc bath before the dross removal of the transition roll in step (1); when the temperature of the zinc bath is 5 - 10 °C higher than the temperature of the zinc bath before the dross removal of the transition roll in step (1), the temperature of the outer plate entering the zinc bath is adjusted to be the same as the current zinc bath temperature.

2. The production method of a high-grade surface galvanized automotive outer panel according to claim 1, characterized in that, In step (1), 1 transition roll is used for skimming and dross removal.

3. The production method of a high-grade surface galvanized automotive outer panel according to claim 1, characterized in that, This method determines the end time of the outer plate in this round according to the strip speed v, specifically as follows: When 95 m / min ≤ strip speed v ≤ 105 m / min, produce 1 more roll of the outer plate in addition to the current roll, and then end the production of the outer plate in this round; When 105 m / min < strip speed v < 115 m / min, produce 1 or 2 more rolls of the outer plate after the current roll has been produced by 50% or more, and then end the production of the outer plate in this round; When 115 m / min ≤ strip speed v ≤ 125 m / min, produce 2 more rolls of the outer plate in addition to the current roll, and then end the production of the outer plate in this round.

4. The production method of a high-grade surface galvanized automotive outer panel according to claim 1, characterized in that, The Al content in the zinc bath is 0.2 - 0.27%, the Fe content is 0.08 - 0.12%, and the strip thickness is 0.7 - 0.85 mm.

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