JPH08323282A - Preparation of coated plated steel sheet - Google Patents

Abstract

PURPOSE: To provide a method for preparing a coated plated steel sheet which can prevent defects of coating from being generated by avoiding the generation of a difference between a target value and the final sheet temp. at the outlet of a heating oven for performing baking of a coating film even if the plating build-up is changed. CONSTITUTION: A plating build-up meter 2, a coating thickness meter 3, a speed detector 5 and a sheet thermometer 6 are provided. A heating quantity calculator 9 collects actual values on plating build-up, film thickness, line speed and sheet temp. at the outlet and calculates an amt. of power-on to an induction heating oven based on these data and sends it to an induction heating oven control device 8 as a set value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a plated steel sheet, and more particularly to control of a heating furnace for baking and drying a plated steel sheet coated with a coating material and for setting the plate temperature after the baking and drying to a final target value. Is.

[0002]

2. Description of the Related Art A cold-rolled steel sheet and a plated steel sheet are coated at a temperature of about 200 ° C. to 400 ° C. after coating a thermosetting paint on the steel sheet.
The coating material is baked by heating with a hot-air heating furnace, an infrared heating furnace, or a high-frequency induction heating furnace so that the temperature becomes ℃. FIG. 2 is a block diagram showing the configuration of an apparatus to which the conventional method for baking a coated steel sheet disclosed in, for example, Japanese Patent Laid-Open No. 63-190681 is applied. In the figure, the coating material coated on the steel strip by the roll coater 1 is first heated in the hot air heating furnace 11, where the solvent is largely evaporated. Furthermore,
The temperature is raised to the target baking temperature in the induction heating furnace 4. The electric power input to the induction heating furnace 4 is the line control computer 1
0, the plate thermometer 12, the plate thermometer 6, and the induction heating furnace control device 8 which receives the output of the heating calorie calculation device 9 which calculates from the data sent from the line speed detector 5.

An apparatus to which a conventional method for baking a coated steel sheet is applied is configured as described above, and the heating calorie calculation apparatus 9 includes, for example, steel sheet data such as sheet thickness and sheet width, sheet temperature at entrance and exit, and line. The amount of heat input to the heating furnace is calculated from the speed and the like, and the calculated value is sent to the induction heating furnace control device 8 to adjust the amount of heating heat of the heating furnace.

[0004]

In the case where the coating film is baked on the plated steel sheet by the conventional method for baking a coated steel sheet as described above, the amount of plating is not taken into consideration.
There is a problem in that a difference occurs between the final plate temperature and the target value, and in a material whose temperature is strictly controlled in terms of quality, coating film defects such as poor coating film adhesion and uneven baking occur.

The present invention has been made in order to solve such a problem, and prevents the difference between the final plate temperature and the target value even if the amount of plating deposit changes, thereby preventing coating film defects. It is an object of the present invention to obtain a method for producing a coated steel sheet which is free from the phenomenon.

[0006]

A method for producing a coated steel sheet according to the present invention comprises a step of plating a steel sheet, a step of applying a coating material to the plated steel sheet, and a step of evaporating a solvent in the coating material applied in a heating furnace. In the method for manufacturing a coated galvanized steel sheet having a step of baking and drying the coating film, a step of measuring the plating adhesion amount and a step of controlling the input heating amount of the heating furnace based on the measured plating adhesion amount. I have it.

[0007]

In the present invention, the amount of plating on the plated steel sheet is measured, the heating amount is calculated in accordance with the amount, and the heating furnace is controlled. Therefore, even if the amount of plating is changed, proper baking of the coating film can be achieved. it can.

[0008]

FIG. 1 is a block diagram showing the construction of an apparatus to which a method for producing a coated plated steel sheet according to an embodiment of the present invention is applied. As a method for applying a coating film, a roll coater system,
An induction heating system is used in a heating furnace for baking and drying the coating film. In the figure, 1, 4, 5, 6, 8, 9, 10 are the same as the conventional ones. In the present embodiment, the plating amount of the plated steel plate 7 formed by plating the steel plate in the plating process (not shown) is measured by the plating amount meter 2. Then, the sheet passing speed is measured by the speed detector 5, the coating film is applied by the roll coater 1, and the film thickness of the coating film is measured by the coating film thickness meter 3. Then, the plated steel sheet is heated by the induction heating furnace 4, and the coating film is baked and dried. The plate temperature of the baked and dried plated steel plate is measured by the plate thermometer 6 installed at the outlet of the heating furnace.

The heating calorie calculation device 9 receives information such as the steel plate size (plate thickness, plate width, etc.) of the steel plate, the target heating plate temperature, etc. from the line control computer 10, and further the plating adhesion amount meter 2, coating film thickness meter. 3, plating amount from speed detector 5 and plate thermometer 6,
Collect actual values such as film thickness, line speed, and outlet plate temperature.
Then, the input electric power of the induction heating furnace is calculated based on these data and sent to the induction heating furnace control device 8 as a set value.
The induction heating furnace control device 8 controls the electric power of the heating coil so that the input electric power is set.

A calculation method in the heating calorie calculation device 9 in the device configured as described above will be specifically described. Let Ti be the plate temperature of the plated steel sheet 7 immediately before entering the induction heating furnace 4, and let To be the outlet target plate temperature of the induction heating furnace 4, and let Piv be the input power required to raise the temperature of the coating steel sheet of Ti to To. To do. This input power Piv is calculated using the following equation (1) when the operating conditions are changed, such as the steel type change and the line speed change. Piv = (Pw + Pm + Pr + Pc + Pvf + Pv + Pvb) / η (1) Pw: Steel plate heating power (KW) Pm: Plating component heating power (KW) Pr: Radiation loss (KW) Pc: Convection loss (KW) Pvf: Coating liquid temperature rise Electric power (before evaporation) (KW) Pv: Coating liquid evaporation power (KW) Pvb: Fixed amount of coating liquid heating (KW) η: Coil efficiency (-) Each term on the right side of the formula (1) is shown below. Calculated by formula. First, the steel plate heating power Pw is calculated using the equation (2). Pw = 3600 × W × Tt × γ × C × V × (To-Ti) / 860 (2) W: Sheet width (m) Tt: Sheet thickness (m) γ: Steel sheet specific gravity (Kg / m ³ ) C : Specific heat of steel plate (Kcal / Kg / ° C) V: Line speed (m / s)

Next, the plating temperature raising power Pm is calculated using the equation (3). Pm = 3600 × W × Tm × γm × Cm × V × (To-Ti) / 860 (3) Tm: Total plating thickness of front and back surfaces (m) γm: Plating material specific gravity (Kg / m ³ ) Cm: Plating Material Specific Heat (Kcal / Kg / ° C.) Next, the radiation loss Pr is calculated using the equation (4). ^{Pr = 2 × 5.67 × 10 -11} × ε × W × Lc × β ... (4) β = (To'-Ti ') 4/5 + (To'-Ti') 3 × Ti '+2 (To' -Ti ') ² × Ti' ² +2 (To'-Ti ') × Ti' ³ + Ti ' ⁴ -T0 ⁴ ε: Emissivity (-) Lc: Coil length (m) To': Absolute heating zone exit Temperature (K) Ti ': Absolute temperature (K) at inlet of heating zone T0: Refractory material temperature (K)

Next, the convection loss Pc is calculated using the equation (5). Pc = 2 × 0.037 × (Va × Lc / ν) ^0.8 × (ν / a / 3600) ^0.6 × W × λ × (To / 2 + Ti / 2-Ta) × Lc / 860 (5) Va: Air Flow velocity (m / s) ν: kinematic viscosity coefficient of air (m ² / s) a: thermal conductivity of air (m ² / h) λ: heat transfer coefficient of air (Kcal / m ² / h / ° C) Ta: Average temperature of air (° C.) To: Heating zone outlet temperature (° C.) Ti: Heating zone inlet temperature (° C.) Next, the coating liquid temperature raising power Pvf is calculated using equation (6). Pvf = 2 × 3600 × Cw × μ × W × V × σw × (100−Ti) × Y / 860 (6) Cw: Specific heat of coating liquid (Kcal / Kg / ° C.) μ: Thickness of coating liquid ( m) σw: Specific gravity of coating liquid (Kg / m ³ ) Y: Ratio of coating liquid (-)

Next, the coating liquid evaporation power Pv is calculated using the equation (7). Pv = 2 × 3600 × μ × W × V × σw × Y × Le / 860 (7) Le: Heat of evaporation (Kcal / Kg) Finally, the formula (8) is used for the coating liquid fixed component heating power Pvb. Calculated. Pvb = 2 × 3600 × Cp × μ × W × V × σw × (To-Ti) × (1-Y) / 860 (8) Cp: Specific heat of fixed amount of coating liquid (Kcal / Kg / ° C.)

The above is the calculation method of the input power set value when the operating conditions such as the amount of plating deposit, the coating film thickness, and the steel plate size change. Next, in a steady state in which the operating conditions do not change, a feedback function is provided to correct the input power set value based on the deviation between the target plate temperature To at the heating zone outlet and the measured value Toj of the plate thermometer 6. That is, when the operating condition is changed (non-steady state), the input power of the induction heating furnace is controlled by the feed forward based on the input power set value and by the feedback during the subsequent steady state.

The difference from the case where the input power is calculated without considering the plating material in the operation of the actual line is, for example, 100 g / m of Zn on one side.
^For double-sided plating of ² (plate width 1 m, line speed 70 mpm
), 18kW (from 400kW to 418kW). This difference in input power is 8 ° C for a steel plate with a thickness of 4 mm.
It appears as a difference (temperature rise) in the baking temperature. In this way, by considering the amount of plating and the coating thickness, it is possible to eliminate the shortage of input power, that is, the shortage of baking temperature, and to reduce the flapping (baking unevenness) of feedback control immediately after the transition from unsteady to steady state. There is also. In the production of coated galvanized steel sheets, which have strict requirements for coating quality such as coating adhesion and uneven baking, how strictly the coating baking temperature can be controlled is particularly important.

In the above examples, the case where the measured value of the coating film thickness was used in addition to the plating amount was explained, but when the control accuracy of the coating film thickness to be applied is good, the coating film thickness is It has been confirmed that the coating thickness target value may be used for calculation without installing a meter. Also, in the above example,
Although a high-frequency induction heating furnace has been illustrated as the heating furnace, the present invention is not limited thereto, and a furnace having another similar function, such as an infrared heating furnace or a hot air heating furnace, may be used.

[0017]

As described above, according to the present invention, since the heating furnace is controlled based on the amount of plating deposit, the controllability of the coating baking temperature is improved. Further, this reduces the defective portion of the coating film and improves the product yield.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an apparatus to which a method for manufacturing a coated plated steel sheet according to an embodiment of the present invention is applied.

FIG. 2 is a configuration diagram of an apparatus to which a conventional method for baking a coated steel sheet is applied.

[Explanation of symbols]

 1: Roll coater 2: Plating adhesion amount meter 3: Coating film thickness gauge 4: Induction heating furnace 5: Speed detector 6: Plate thermometer 7: Plating steel plate 8: Induction heating furnace control device 9: Heating calorie calculation device 10 : Line control computer 11: Hot air heating furnace 12: Plate thermometer

Claims (1)

[Claims] 1. A coated galvanized steel sheet comprising a step of plating a steel sheet, a step of applying a coating material to the plated steel sheet, and a step of evaporating a solvent in the coating material applied in a heating furnace to bake and dry the coating film. In the manufacturing method, there is a step of measuring the plating adhesion amount of the plating steel sheet after plating and before the coating of the coating material, and a step of controlling the input heating amount of the heating furnace based on the measured plating adhesion amount. Manufacturing method of coated steel sheet.