JPS6058302B2 - Method for predicting molten metal solidification position in continuous molten plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for predicting the solidification position of molten metal on the surface of a steel strip after plating in continuous hot-dip plating of a steel strip.

For example, in the method of manufacturing galvanized steel sheets using continuous hot-dip galvanizing equipment, the steel strip leaving the continuous annealing furnace is heated in a hot-dip zinc bath.
After passing through a plating bath (hereinafter referred to as a plating bath), while the zinc adhering to the steel strip is in a molten state, the amount of zinc adhering is adjusted using a gas injection nozzle, and then cooling is performed using a cooling device.

When manufacturing minimum spangle (also called zero spangle) galvanized steel sheets using this manufacturing method,
After adjusting the amount of zinc deposited, and just before the molten zinc on the surface of the steel strip solidifies, the steel strip is passed through a minimum spangle device (a device that sprays water with a chemical added thereto). When manufacturing ordinary galvanized steel sheets with spangles, the solidification position of molten zinc on the surface of the steel strip (position viewed in the direction of steel strip progress) after adjusting the amount of zinc coating using a gas injection nozzle is determined after the cooling device. If this happens, there will be a problem that zinc will adhere to the rolls of the cooling device.

In addition, when manufacturing minimum spangle galvanized steel sheets, if the solidification position of molten zinc on the surface of the steel strip is not within the movement adjustment range of the minimum spangle device that can move in the direction of steel strip movement, it is necessary to cannot produce minimum spangle products. In other words, the minimum
If the zinc on the surface of the steel strip is not solidified while passing through the spangle device, the surface of the deposited zinc will have a bit-like rough appearance, and the zinc on the surface of the steel strip will have already solidified before entering the minimum spangle device. When there is a spangle will occur.
For these reasons, the solidification position of the molten zinc on the steel strip surface after adjusting the amount of zinc deposited by the gas injection nozzle is in front of the cooling device, and when manufacturing mini-spangle products, it passes through the spangle device at a minimum. It is required that the state of solidification of zinc on the surface of the steel strip be appropriate. The solidification position of molten zinc on the surface of the steel strip after adjusting the amount of zinc deposited using a gas injection nozzle is determined by the amount of zinc deposited, the dimensions of the steel strip (thickness, width),
It varies depending on the speed of the steel strip, the temperature of the steel strip on the exit side of the annealing furnace (on the plating bath side), the temperature of the plating bath, etc. It also depends on the pressure and temperature of the gas injected from the gas injection nozzle, the temperature of the atmosphere, etc. It always changes.

The steel strips to be plated, including those of different dimensions and materials, are rolled up into coils and then welded one after the other and are passed through the steel strip continuously, so the dimensions, speed, and temperature of the steel strip vary from coil to coil, and the amount of zinc deposited varies from coil to coil. The pressure changes for each coil or several times within the same coil, and the pressure of the gas injected from the gas injection nozzle is changed in accordance with the amount of zinc deposited. Furthermore, the temperature of the plating bath, the temperature of the gas injected from the gas injection nozzle, the temperature of the atmosphere, etc. also vary. In this way, the solidification position of the molten zinc on the surface of the steel strip changes frequently and in a complicated manner, but in the past, there was no suitable method for predicting the solidification position of the molten zinc, so workers had to visually check the solidification position. They observed this and empirically adjusted the speed of the steel strip so that the solidification position was within the appropriate range, and also adjusted the movement of the minimum spangle device so that it was in the appropriate position. . However, this adjustment method by the operator requires a heavy burden on the operator to constantly observe the coagulation position, which changes frequently, and it is difficult to accurately predict the coagulation position, which changes in a complicated manner, or to adjust the speed. However, problems such as poor appearance of plated products and adhesion of zinc to the rolls of cooling equipment have occurred. The present invention provides a method for predicting the solidification position in order to solve the problems in the conventional method as described above. In continuous hot-dip plating of steel strip using the equipped molten metal plating equipment, the temperature of the steel strip on the exit side of the molten metal bath is calculated using the temperature of the steel strip on the exit side of the annealing furnace, the temperature of the molten metal bath, and the thickness of the steel strip. The melting on the surface of the steel strip is calculated using the amount of heat removed from the steel strip by the gas injection, the sensible heat retained by the steel strip, and the latent heat of solidification of the molten metal. This is a method for predicting the solidification position of molten metal in continuous hot-dip plating, which is characterized by calculating the solidification position of molten metal as the distance from the molten metal bath surface in the steel strip traveling direction.

゛Hereinafter, the present invention will be explained in detail based on an example in which the present invention is applied to continuous hot-dip galvanizing.

FIG. 1 is a diagram showing the configuration of main parts of galvanizing equipment and an example of the arrangement of various measuring instruments necessary for carrying out the method of the present invention. In FIG. 1, a steel strip 2 is annealed in an annealing furnace 1, and its temperature is measured with a thermometer 3 provided on the exit side of the annealing furnace. 4 is a plating bath, and the temperature of the plating bath 5 is measured with a thermometer 6.

The amount of zinc deposited on the steel strip 2 that has passed through the plating bath 5 is adjusted by a gas injection nozzle 7. 10 is a pressure regulator for the injected gas, 9 is a pressure gauge, 11 is a control valve, and 8 is a thermometer for measuring the temperature of the injected gas.

The steel strip 2 whose zinc coating amount has been adjusted passes through a minimum spangle device 12. The minimum spangle device 12 is movable in the steel strip traveling direction (vertical direction) and the steel strip width direction by a moving device 13, and is inserted so as to sandwich the nozzle in the device against the steel strip 2. Thereafter, the naturally air-cooled steel strip 2 is cooled by the cooling device 15. 16 is steel strip 2
17 is a zinc-coated coating amount measuring device.

FIG. 2 shows the temperature drop of the steel strip passing through each device in the facility shown in FIG.

Tsf is the temperature on the exit side of the annealing furnace, and Tspi is the temperature on the plating bath entry side. However, the area from the annealing furnace exit side to the plating bath side is sealed and there is almost no temperature drop, so T
It is safe to assume that spi and Tsf are equal. Next, heat is removed from the steel strip by convection heat transfer within the plating bath, and the temperature of the steel strip drops from the inlet temperature Tspi to the outlet temperature TspO. The temperature TspO at this time is the inlet temperature Tspi(Tsf
) and varies depending on the plating bath temperature, steel strip speed, plate thickness, etc. The distance from the plating bath surface to the gas injection nozzle for adjusting the amount of zinc deposited is usually about 200 Tm, so the temperature drop during this distance is small and the temperature of the steel strip is equal to the temperature Ts at the exit side of the plating bath.
It is safe to assume that the gas reaches the gas injection nozzle while remaining at pO. Next, heat is removed from the steel strip in a short time by the gas injected from the gas injection nozzle, and the temperature of the steel strip drops to Tsn. The amount of temperature drop at this time varies depending on the temperature TspO of the steel strip, the temperature and weight of the injected gas, and the like. From the gas injection nozzle to the entrance of the minimum ● spangle device,
The temperature of the steel strip drops to Tse due to radiation. minimum·
In the spangle device, the steel strip is sprayed with minimum spangle liquid to remove heat in a short period of time, and the temperature of the steel strip drops to the freezing point of molten zinc. In the case of normal galvanized steel sheet production with spangles, the minimum spangle device shown in Figure 1 is evacuated from the steel strip threading path, and the steel strip is placed in the cooling device 1.
It is naturally cooled down to 5 (indicated by the dotted line in Figure 2).
.

Now, a method of calculating the solidification position of molten zinc on the surface of the steel strip after adjusting the amount of zinc deposited by the gas injection nozzle in such a galvanizing line will be described using various measurement results. Calculation of the solidification position of molten zinc is performed according to procedures (1) to (5) described below. (1) Calculation of the temperature TspO of the steel strip when it comes out of the plating bath, where Cs:
Specific heat of the steel strip (constant) ρs: Density of the steel strip (constant) t: Thickness of the steel strip (variable...nominal value) ■: Speed of the steel strip (variable...actual value) Hp: Inside the plating bath Convection heat transfer coefficient (constant) between molten zinc and steel strip 1: Length of steel strip in plating bath (constant) Tzp: Temperature of plating bath (variable...actual value) Tsf:
Temperature of the steel strip on the exit side of the annealing furnace (variable...actually measured value) (2)
Calculation of the amount of heat Qn taken away by the gas from the gas injection nozzle where G: Weight flow rate of the injection gas P: Pressure of the injection gas (variable...actual value) g: Acceleration of gravity (constant) ρ: Density of the injection gas ( (constant) Tg: Temperature of the injected gas (variable... actually measured value) PO: Atmospheric pressure (constant) SO: Opening area of the gas injection nozzle (constant) where Wn: Width of the gas injection nozzle (constant) Cg: Injection Specific heat of gas (constant) W: Width of steel strip (variable...nominal value) (3) Calculation of sensible heat QS of steel strip --- Here, W
: Width of steel strip (variable...nominal value) TsO: Temperature of steel strip when molten zinc solidifies (constant...? Same as coagulation temperature TO of molten zinc) (4) Solidification of molten zinc Calculation of the amount of heat generated by
) Calculation of the amount of heat Qe removed by spraying the minimum spangle liquid, where h: Minimum Heat transfer coefficient (constant) between the spangle liquid and the steel strip L: Minimum Effective spraying length of the spangle liquid (constant) Tw: Minimum Spangle liquid spraying temperature (constant) (6) Solidification position of molten zinc on the steel strip surface
Calculation The amount of heat loss Qr due to radiation in the steel strip from the outlet side of the plating bath to the minimum spangle device is given by Tse, the temperature of the steel strip immediately before the minimum spangle device, where: σ: Stephann Boltzmann constant here where, Ta: atmospheric temperature (variable: actually measured value) Figure 3 shows the above calculation procedure in a diagram.

By the above procedure, the solidification position of molten zinc on the surface of the steel strip (distance x in the steel strip traveling direction as seen from the plating bath surface) after adjusting the amount of zinc deposited by gas injection is determined at appropriate intervals.

When producing a normal galvanized steel sheet with spangles, check whether the solidification position (distance When manufacturing, it is checked whether the movement adjustment range of the minimum spangle device is exceeded. If it is not exceeded, the speed of the steel strip remains as it is, and if it is exceeded, the solidification position is set to a predetermined position ( The speed is corrected by finding the speed Vp of the steel strip such that it does not exceed the speed Vp. However, Qr=
Qs+Qm-Qn-Qe It is appropriate to perform the above series of calculations using a computer, and the speed correction can be automated by an automatic controller.

As described above, according to the present invention, the solidification position of molten zinc on the surface of the steel strip after leaving the plating bath is predicted, and the speed of the steel strip is corrected as necessary, thereby improving the appearance of the plated product and improving the cooling system. It is possible to prevent plating metal from adhering to the roll. Although the above description has been made using continuous hot-dip galvanizing as an example, the present invention is not limited to galvanizing, and can of course be applied to other hot-dip metal plating such as tin plating and aluminum plating.

[Brief explanation of drawings]

Figure 1 is a diagram showing the configuration of the main parts of galvanizing equipment and an example of the arrangement of various measuring instruments necessary for implementing the present invention, and Figure 2 is a diagram showing the temperature drop of the steel strip passing through each device in the equipment shown in Figure 1. A diagram showing the situation,
FIG. 3 is a diagram showing a calculation procedure in an embodiment of the present invention. 1... Annealing furnace, 2... Steel strip, 3...
...Thermometer, 4...Plated bathtub, 5...
Plating bath, 6...Thermometer, 7...Gas injection nozzle, 8...Thermometer, 9...Pressure gauge, 10...・Pressure regulator, 11...
Control valve, 12... Minimum spangle device, 13
...Movement device, 14...Roll, 15.
...Cooling device, 16...Speedometer, 17...
...Zinc adhesion measuring device.

Claims (1)

[Claims] 1. In continuous hot-dip plating of a steel strip using a hot-dip metal plating equipment equipped with a continuous annealing furnace, a molten metal bath, a plating coating amount adjustment device using gas injection, etc., the temperature and melting of the steel strip on the exit side of the annealing furnace The temperature of the steel strip on the outlet side of the molten metal bath is calculated using the temperature of the metal bath, the thickness and speed of the steel strip, and the amount of heat taken away from the steel strip by the gas injection and the sensible heat possessed by the steel strip are calculated. The solidification position of the molten metal on the surface of the steel strip is calculated as the distance in the steel strip traveling direction from the molten metal bath surface by calorific value calculation using the latent heat of solidification of the molten metal. Method for predicting coagulation location. 2. The method for predicting the solidification position of molten metal in continuous hot-dip plating according to claim 1, wherein the continuous hot-dip plating is hot-dip galvanizing.